Showing 1–50 of 133 results for author: Matsuda, M

Spin nematic liquid crystal and scalar spin chirality in tetragonal lattice YbMnBi$_2$

Authors: Yaofeng Xie, Sijie Xu, Yu Pan, Taekoo Oh, Tingjun Zhang, Masaaki Matsuda, Zhaoyu Liu, Zehao Wang, Yiheng Wang, Siyu Pan, Avishek Maity, Sylwia Pawledzio, Xiaoping Wang, Songxue Chi, Feng Ye, Yiqing Hao, Huibo Cao, Barry L. Winn, Melissa K. Graves-Brook, Shuai Wu, Fan Li, Xiaoyuan Zhou, Claudia Felser, Naoto Nagaosa, Pengcheng Dai

Abstract: A spin nematic order, analogous to the nematic liquid crystal, characterizes the spontaneous breaking of spin-space rotational symmetry while preserving time-reversal ($T$) symmetry. In contrast, scalar spin chirality (SSC), a composite three-spin order, breaks $T$ symmetry and is known to induce an anomalous Hall effect (AHE). Although a spin nematic phase has been suggested in frustrated magnets… ▽ More A spin nematic order, analogous to the nematic liquid crystal, characterizes the spontaneous breaking of spin-space rotational symmetry while preserving time-reversal ($T$) symmetry. In contrast, scalar spin chirality (SSC), a composite three-spin order, breaks $T$ symmetry and is known to induce an anomalous Hall effect (AHE). Although a spin nematic phase has been suggested in frustrated magnets and the square-lattice iridate, how it might affect magnetotransport properties is unknown. Here we use polarized neutron scattering to show that tetragonal $A$MnBi$_2$ ($A$ = Ca, Yb) is a strictly $c$-axis-aligned collinear antiferromagnet (C-type), with $T_N \approx 270$ K and 290 K, respectively. On cooling from 450 K to $T_N$, low-energy spin excitations in YbMnBi$_2$ spontaneously change from isotropic to anisotropic in spin space within the tetragonal plane, forming a dynamic spin nematic phase around 400 K due to heavy Yb-induced spin-orbit coupling, before gapping out below $T_N$. Similar measurements on CaMnBi$_2$ reveal isotropic paramagnetic scattering without a spin nematic phase above $T_N$. Under an in-plane magnetic field, the Yb$^{3+}$ moments may interact with the dynamic spin nematic phase to induce nonzero SSC, giving rise to AHE and an anomalous Nernst effect (ANE) in YbMnBi$_2$ that are absent in CaMnBi$_2$ above $T_N$. A symmetry-based Ginzburg-Landau analysis shows that coupling terms between the nematic order and SSC are allowed under an external magnetic field, which could explain the rapid increase of AHE with field in YbMnBi$_2$. Our results provide compelling evidence for dynamic SSC-induced AHE and ANE in the paramagnetic phase of a compensated collinear antiferromagnet, opening a new avenue for the physics of composite spin orders and room-temperature spintronics without magnetic order. △ Less

Submitted 12 August, 2026; originally announced August 2026.

Orbital-selective oxygen holes in cuprate ladders beyond the Zhang-Rice paradigm

Authors: Chengyun Hua, Tianran Chen, Isaac C. Ownby, Colin L. Sarkis, Garrett Granoth, Masaaki Matsuda, Jiaqiang Yan, Ho Nyung Lee, Jeongkeun Song, Yuya Shinohara, Masatomo Uehara, Jun Akimitsu, Oleksandr Prokhnenko, Eugen Weschke, Takeshi Egami, D. Alan Tennant

Abstract: The electronic structure of the spin-ladder cuprate Sr14Cu24O41 challenges the presumed universality of the Zhang-Rice singlet (ZRS) framework and models based exclusively on Cu-O hybridized orbitals. Combining polarization-dependent resonant soft X-ray scattering at the O K-edge with inelastic neutron scattering, we show that doped holes in the Cu2O3 ladders localize predominantly in planar non-b… ▽ More The electronic structure of the spin-ladder cuprate Sr14Cu24O41 challenges the presumed universality of the Zhang-Rice singlet (ZRS) framework and models based exclusively on Cu-O hybridized orbitals. Combining polarization-dependent resonant soft X-ray scattering at the O K-edge with inelastic neutron scattering, we show that doped holes in the Cu2O3 ladders localize predominantly in planar non-bonding O 2pz (pπ) orbitals of rung oxygen sites rather than forming conventional ZRS states. Polarization-resolved RSXS uniquely identifies this orbital assignment, while lattice and magnetic excitations reveal its coupled consequences, establishing a unified microscopic picture that excludes the conventional σ-bonded singlet. This oxygen-sublattice charge order produces an anomalous diagonal stretching phonon and explains the absence of incommensurate magnetic fluctuations and anomalous magnon splitting. These findings motivate a reassessment of hole pairing in ladder cuprates and the sufficiency of copper-centric models for cuprate superconductors. △ Less

Submitted 10 August, 2026; originally announced August 2026.

$d$-spacing distributions as a probe of nematoelastic response in iron-based superconductors

Authors: Wenting Zhang, Ruixian Liu, Tingjun Zhang, Weiliang Yao, Xüe Fu, Hanqing Xie, Ziye Mo, Ting Guo, Kuo-Feng Tseng, Thomas Keller, Jitae T. Park, Fankang Li, Masaaki Matsuda, Avishek Maity, Long Tian, Pengcheng Dai, Xingye Lu

Abstract: Electronic nematicity in iron-based superconductors (FeSCs) couples bilinearly to orthorhombic strain, allowing nematic correlations to appear in the lattice response. Here we use neutron Larmor diffraction to measure the temperature-dependent distribution of relative $d$ spacings in electron-doped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, hole-doped Ba$_{0.83}$K$_{0.17}$Fe$_2$As$_2$, FeSe, and Fe$_{1.07}$T… ▽ More Electronic nematicity in iron-based superconductors (FeSCs) couples bilinearly to orthorhombic strain, allowing nematic correlations to appear in the lattice response. Here we use neutron Larmor diffraction to measure the temperature-dependent distribution of relative $d$ spacings in electron-doped Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$, hole-doped Ba$_{0.83}$K$_{0.17}$Fe$_2$As$_2$, FeSe, and Fe$_{1.07}$Te. In Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ crystals without intentionally applied uniaxial stress, the in-plane distribution width, $\varepsilon_{\rm FWHM}$, increases on cooling in the tetragonal phase and can be described phenomenologically by a Curie--Weiss-like form. The fitted scale $T^*$ decreases with Co doping and evolves similarly to the nematic phase diagram inferred from elastoresistance, although the two experiments probe different response functions. Related broadening in Ba$_{0.83}$K$_{0.17}$Fe$_2$As$_2$ and FeSe supports extending this interpretation beyond electron-doped BaFe$_2$As$_2$. By contrast, Fe$_{1.07}$Te shows no extended Curie--Weiss-like regime without applied stress, whereas uniaxial pressure produces a strongly anisotropic broadening that can contain contributions from both the field-biased lattice response and inhomogeneous loading. A mean-field model with bilinear nematoelastic coupling and spatially varying symmetry-breaking stress explains the Curie--Weiss-like broadening in terms of the renormalized orthorhombic compliance. Neutron Larmor diffraction therefore provides a bulk-sensitive probe of nematic-related lattice broadening that complements electronic and elastic measurements. △ Less

Submitted 2 August, 2026; originally announced August 2026.

Comments: 9 pages, 4 figures

Doping-induced Ferromagnetic order and its unusual evolution to Helical Antiferromagnetic Order in Sr(Ni$_{1-x}$Co$_x$)$_2$P$_2$

Authors: A. Sapkota, J. Schmidt, J. M. Wilde, L. -L. Wang, W. Tian, M. Matsuda, A. Kreyssig, S. L. Bud'ko, P. C. Canfield

Abstract: SrNi$_2$P$_2$ represents a unique case of a collapsed structural phase (one-third collapsed, where one out of every three P-P pairs forms a bond) in the A(TM)$_2$X$_2$ family of compounds (A = alkali metal, alkaline-earth metal, or rare earth; TM = transition metal; X = pnictogen). Furthermore, Co doping studies aimed at understanding the interrelationship between this unusual bonding motif and th… ▽ More SrNi$_2$P$_2$ represents a unique case of a collapsed structural phase (one-third collapsed, where one out of every three P-P pairs forms a bond) in the A(TM)$_2$X$_2$ family of compounds (A = alkali metal, alkaline-earth metal, or rare earth; TM = transition metal; X = pnictogen). Furthermore, Co doping studies aimed at understanding the interrelationship between this unusual bonding motif and the resulting physical properties produced a magnetically rich phase diagram, specifically on the Co-rich side of the phase diagram. However, important questions remained regarding the detailed nature of the magnetic ground states. To address these issues, we performed single-crystal neutron diffraction measurements on Sr(Ni$_{1-x}$Co$_x$)$_2$P$_2$ with compositions $x = 0.88$, 0.94, and 0.97. For $x = 0.88$ and 0.94, the measurements reveal incommensurate helical magnetic order with a doping-dependent propagation vector $(0,0,τ)$, similar to that observed in Sr(Ni$_{1-x}$Co$_x$)$_2$As$_2$. In contrast, the $x = 0.97$ composition shows clear signatures of a ferromagnetically ordered ground state, resolving the earlier ambiguity regarding the nature of the low-temperature phase. Furthermore, our results highlight the subtle balance between these competing ground states, whose evolution does not appear to be fully captured by the conventional frameworks of either itinerant or local-moment Heisenberg models typically applied to related 122 systems. △ Less

Submitted 22 July, 2026; originally announced July 2026.

Comments: 10 pages, 8 figures

Incommensurate Antiferromagnetic Order in the Fe-substituted Bi-2201 Cuprate in the Heavily Overdoped Regime

Authors: Y. Komiyama, Y. Ikeda, T. Taniguchi, T. J. Williams, M. Matsuda, S. Asai, T. Masuda, H. Kuwahara, H. Kuroe, T. Kawamata, I. Watanabe, M. Fujita, T. Adachi

Abstract: Elastic neutron scattering experiments showed incommensurate antiferromagnetic peaks in 5% Fe-substituted Bi-2201 cuprate in the non-superconducting heavily overdoped regime. The incommensurability delta~0.21 is comparable to that observed in Fe-substituted Bi-2201 in the overdoped regime. [Hiraka et al., Phys. Rev. B 81, 144501 (2010).] The magnetic correlation length is comparable between the ov… ▽ More Elastic neutron scattering experiments showed incommensurate antiferromagnetic peaks in 5% Fe-substituted Bi-2201 cuprate in the non-superconducting heavily overdoped regime. The incommensurability delta~0.21 is comparable to that observed in Fe-substituted Bi-2201 in the overdoped regime. [Hiraka et al., Phys. Rev. B 81, 144501 (2010).] The magnetic correlation length is comparable between the overdoped and non-superconducting heavily overdoped regimes. It is plausible that incommensurate antiferromagnetic order is induced and stabilized by Fe in the heavily overdoped regime, which suggests a robust antiferromagnetic correlation beyond the superconducting dome in the phase diagram. △ Less

Submitted 16 May, 2026; originally announced May 2026.

Comments: 5 pages, 3 figures, J. Phys. Soc. Jpn., in press

Journal ref: J. Phys. Soc. Jpn. 95, 073701 (2026)

Collinear ferromagnetism with reduced moment length in kagome magnet Nd3Ru4Al12

Authors: Yuki Ishihara, Ryota Nakano, Rinsuke Yamada, Takuya Nomoto, Priya R. Baral, Moritz M. Hirschmann, Kamini Gautam, Kamil K. Kolincio, Akiko Kikkawa, Seno Aji, Hiraku Saitoh, Masaaki Matsuda, Yasujiro Taguchi, Taka-hisa Arima, Yoshinori Tokura, Taro Nakajima, Max Hirschberger

Abstract: We determine the magnetic ground state of the kagome lattice magnet Nd3Ru4Al12 by single-crystal neutron diffraction, supported by experiments with polarized neutrons. We identify this material as a collinear ferromagnet ("hex-FM") with uniform moment length mc = 2.1 μB/Nd and ordering vector Q = 0, in contrast to a previous, seminal report that proposed unequal moment lengths on two Nd sites, her… ▽ More We determine the magnetic ground state of the kagome lattice magnet Nd3Ru4Al12 by single-crystal neutron diffraction, supported by experiments with polarized neutrons. We identify this material as a collinear ferromagnet ("hex-FM") with uniform moment length mc = 2.1 μB/Nd and ordering vector Q = 0, in contrast to a previous, seminal report that proposed unequal moment lengths on two Nd sites, here called the "ortho-FM" state. Our analysis of the flipping ratio in polarized neutron scattering is consistent with the hex-FM state. The results provide a microscopic basis for understanding the large fluctuation-induced Hall and Nernst responses near TC = 41 K, as previously reported for Nd3Ru4Al12. △ Less

Submitted 2 June, 2026; v1 submitted 2 May, 2026; originally announced May 2026.

Comments: 15 pages, 6 figures

Journal ref: Phys. Rev. B 113, 214410 (2026)

Quasi-one-dimensional spin excitations in the iron pnictide NaFe$_{0.53}$Cu$_{0.47}$As

Authors: Yifan Wang, David W. Tam, Weiyi Wang, R. A. Ewings, J. Ross Stewart, Masaaki Matsuda, Chongde Cao, Changle Liu, Rong Yu, Pengcheng Dai, Yu Song

Abstract: Spectroscopic measurements in model one-dimensional (1D) correlated systems offer insights for understanding their two-dimensional counterparts, which include the cuprate and iron pnictide/chalcogenide superconductors. A major challenge is the identification of such correlated systems with dominantly 1D physics. In this work, inelastic neutron scattering measurements on NaFe$_{0.53}$Cu$_{0.47}$As… ▽ More Spectroscopic measurements in model one-dimensional (1D) correlated systems offer insights for understanding their two-dimensional counterparts, which include the cuprate and iron pnictide/chalcogenide superconductors. A major challenge is the identification of such correlated systems with dominantly 1D physics. In this work, inelastic neutron scattering measurements on NaFe$_{0.53}$Cu$_{0.47}$As single crystal directly reveal quasi-1D spin excitations, resulting from atomic order that lead to magnetic Fe and nonmagnetic Cu chains. The dominant exchange interaction is antiferromagnetic along the chain ($SJ_{\rm \parallel}\approx90.1(3)$~meV), whereas the inter-chain couplings are much weaker ($SJ_{\rm \perp}\approx-2.4(1)$~meV and $SJ_{\rm c}\approx0.15(5)$~meV). The quasi-1D spin excitations in NaFe$_{0.53}$Cu$_{0.47}$As stem from both the Néel and stripe vectors, with Néel excitations sensitive to Fe impurities on the Cu site. The spin excitations in quasi-1D NaFe$_{0.53}$Cu$_{0.47}$As and quasi-2D FeSe exhibit a striking resemblance, suggesting a common origin for their coexistent stripe and Néel excitations. Our findings demonstrate magnetic dilution in NaFeAs leads to dimension reduction of its magnetic degree of freedom, presenting a strategy for discovering low-dimensional quantum materials. △ Less

Submitted 6 February, 2026; originally announced February 2026.

Comments: supplementary information available upon request

Journal ref: Phys. Rev. Lett. 136, 066503 (2026)

Coherent high-velocity chiral magnons in the metallic altermagnet CrSb

Authors: Ashutosh K. Singh, Niclas Heinsdorf, Abraham A. Mancilla, Jörn Bannies, Avishek Maity, Alexander I. Kolesnikov, Masaaki Matsuda, Matthew B. Stone, Marcel Franz, Jonathan Gaudet, Alannah M. Hallas

Abstract: We report the collective magnetism of the metallic altermagnet CrSb. Magnetic susceptibility and polarized neutron diffraction measurements show that CrSb is a perfectly compensated Ising altermagnet below a Néel temperature of $T_N = 733(4)$ K. Inelastic neutron scattering experiments reveal coherent and highly-dispersive antiferromagnetic spin waves with large group velocities of 61(2) km s… ▽ More We report the collective magnetism of the metallic altermagnet CrSb. Magnetic susceptibility and polarized neutron diffraction measurements show that CrSb is a perfectly compensated Ising altermagnet below a Néel temperature of $T_N = 733(4)$ K. Inelastic neutron scattering experiments reveal coherent and highly-dispersive antiferromagnetic spin waves with large group velocities of 61(2) km s$^{-1}$ and 58(2) km s$^{-1}$ along the in-plane and out-of-plane directions, respectively. The observed magnon dispersions along high-symmetry directions of the Brillouin zone are well described by a minimal Heisenberg model up to third nearest neighbors of alternating antiferromagnetic and ferromagnetic character, $J_1 = 23(4)$ meV, $J_2 = -5.4(8)$ meV, $J_3 = 5.2(8)$ meV, and an Ising single-ion anisotropy term $D = 0.15(4)$ meV. We observe clear momentum space signatures of chiral spin splitting along the low-symmetry $Γ$-$L$ direction, characteristic of higher-order altermagnetic exchange interactions, the first such observation in a metallic altermagnet. These findings identify CrSb as a singular material: a metallic altermagnet in which coherent spin-split magnons persist well above room temperature, providing a compelling platform for spintronic applications. △ Less

Submitted 13 May, 2026; v1 submitted 20 November, 2025; originally announced November 2025.

Magnetism and Peierls distortion in Dirac semimetal CaMnBi$_2$

Authors: Aashish Sapkota, Niraj Aryal, Xiao Hu, Masaaki Matsuda, Yan Wu, Guangyong Xu, John M. Wilde, Andreas Kreyssig, Paul C. Canfield, Cedomir Petrovic, John M. Tranquada, Igor A. Zaliznyak

Abstract: Dirac semimetals of the form $A$Mn$X_2$ ($A =$ alkaline-earth or divalent rare earth; $X =$ Bi, Sb) host conducting square-net Dirac-electron layers of $X$ atoms interleaved with antiferromagnetic Mn$X$ layers. In these materials, canted antiferromagnetism can break time-reversal symmetry (TRS) and produce a Weyl semimetallic state. CaMnBi$_2$ was proposed to realize this behavior below… ▽ More Dirac semimetals of the form $A$Mn$X_2$ ($A =$ alkaline-earth or divalent rare earth; $X =$ Bi, Sb) host conducting square-net Dirac-electron layers of $X$ atoms interleaved with antiferromagnetic Mn$X$ layers. In these materials, canted antiferromagnetism can break time-reversal symmetry (TRS) and produce a Weyl semimetallic state. CaMnBi$_2$ was proposed to realize this behavior below $T^{*}\sim 50$ K, where anomalies in resistivity and optical conductivity were reported. We investigate single-crystal CaMnBi$_{2}$ using polarized and unpolarized neutron diffraction, x-ray diffraction, and density functional theory (DFT) calculations to elucidate the underlying crystal and magnetic structures. The results show that the observed anomalies do not originate from spin canting or weak ferromagnetism; no measurable uniform Mn spin canting is detected. Instead, CaMnBi$_2$ undergoes a coupled structural and magnetic symmetry-lowering transition at $T^{*} = 46(2)$ K, from a tetragonal lattice with C-type antiferromagnetism to an orthorhombic phase with unit-cell doubling along the $c$ axis and minimal impact on magnetism. Analysis of superlattice peak intensities and lattice distortion reveals a continuous second-order transition governed by a single order parameter. The refined atomic displacements correspond to a zigzag bond-order-wave (BOW) modulation of Bi-Bi bonds, consistent with an electronically driven Peierls-type instability in the Dirac-electron Bi layer, long anticipated by Hoffmann and co-workers [W.~Tremel and R.~Hoffmann, \textit{J. Am. Chem. Soc.} \textbf{109}, 124 (1987); G.~A.~Papoian and R.~Hoffmann, \textit{Angew. Chem. Int. Ed.} \textbf{39}, 2408 (2000)]. %\textcite{TremelHoffman_JACS1987} [JACS {\bf 109}, 124 (1987)]. △ Less

Submitted 5 November, 2025; originally announced November 2025.

Comments: 25 pages with 19 figures including appendices; 15 pages, 11 figs main text

Non-Altermagnetic Origin of Exchange Bias Behaviors in Incoherent RuO$_2$/Fe Bilayer Heterostructures

Authors: Shelby S. Fields, Joseph C. Prestigiacomo, Cory D. Cress, Nicholas G. Combs, Olaf van 't Erve, Patrick G. Callahan, Keith E. Knipling, Michelle E. Jamer, Frank M. Abel, Feng Ye, Arianna Minelli, Zachary J. Morgan, Haile Ambaye, Masaaki Matsuda, Avishek Maity, Valeria Lauter, Steven P. Bennett

Abstract: Initially identified as a promising altermagnetic (AM) candidate, rutile RuO$_2$ has since become embroiled in controversy due to contradictory findings of modeling and measurements of the magnetic properties of bulk crystals and thin films. For example, despite observations of a bulk non-magnetic state using density functional theory, neutron scattering, and muon spin resonance measurements, patt… ▽ More Initially identified as a promising altermagnetic (AM) candidate, rutile RuO$_2$ has since become embroiled in controversy due to contradictory findings of modeling and measurements of the magnetic properties of bulk crystals and thin films. For example, despite observations of a bulk non-magnetic state using density functional theory, neutron scattering, and muon spin resonance measurements, patterned RuO$_2$ Hall bars and film heterostructures display magnetotransport signatures of magnetic ordering. Among the characteristics routinely cited as evidence for AM is the observation of exchange bias (EB) in an intimately contacted Fe-based ferromagnetic (FM) layer, which can arise due to interfacial coupling with a compensated antiferromagnet. Within this work, the origins of this EB coupling in Ru-capped RuO$_2$/Fe bilayers are investigated using polarized neutron diffraction, polarized neutron reflectometry, cross-sectional transmission electron microscopy, and super conducting quantum interference device measurements. These experiments reveal that the EB behavior is driven by the formation of an iron oxide interlayer containing Fe$_3$O$_4$ that undergoes a magnetic transition and pins interfacial moments within Fe at low temperature. These findings are confirmed by comparable measurements of Ni-based heterostructures, which do not display EB coupling, as well as magnetometry of additional Fe/Ru bilayers that display oxide-driven EB coupling despite the absence of the epitaxial RuO$_2$ layer. While these results do not directly refute the possibility of AM ordering in RuO$_2$ thin films, they reveal that EB, and related magnetotransport phenomena, cannot alone be considered evidence of this characteristic in the rutile structure due to interfacial chemical disorder. △ Less

Submitted 26 September, 2025; originally announced September 2025.

Comments: 20 pages, 7 figures

Magnetic excitations from the hexagonal spin clusters in the S = 1/2 distorted honeycomb lattice antiferromagnet Cu2(pymca)3(ClO4)

Authors: Masaaki Matsuda, Alexander I. Kolesnikov, Zentaro Honda, Tokuro Shimokawa, Sho Inoue, Yasuo Narumi, Masayuki Hagiwara

Abstract: Cu2(pymca)3(ClO4) (pymca: pyrimidine-2-carboxylate) consists of a slightly distorted honeycomb lattice of Cu2+ spins, which shows no long-range magnetic order down to 0.6 K. A magnetization study revealed 1/3 and 2/3 plateau phases [A. Okutani et al., J. Phys. Soc. Jpn. 88, 013703 (2019)], which is not expected for regular honeycomb antiferromagnets. Inelastic neutron scattering experiments were p… ▽ More Cu2(pymca)3(ClO4) (pymca: pyrimidine-2-carboxylate) consists of a slightly distorted honeycomb lattice of Cu2+ spins, which shows no long-range magnetic order down to 0.6 K. A magnetization study revealed 1/3 and 2/3 plateau phases [A. Okutani et al., J. Phys. Soc. Jpn. 88, 013703 (2019)], which is not expected for regular honeycomb antiferromagnets. Inelastic neutron scattering experiments were performed using a powder sample to investigate the exchange interactions of this material. The spin excitations from the singlet ground state to the first three triplet states, predicted from the antiferromagnetic hexagonal spin cluster interacting with 3.9 meV, were observed. Using the exact diagonalization mothods, the intercluster coupling was estimated from the excitation peak width to be about 20% of the intracluster interaction, which is consistent with the previously reported value. Our exchange path model explains the anisotropic exchange interactions in the distorted honeycomb plane. △ Less

Submitted 29 May, 2025; v1 submitted 25 April, 2025; originally announced April 2025.

Comments: 6 pages, 6 figures

Journal ref: Physical Review B 111, 224430 (2025)

Nature of the ferromagnet-paramagnet transition in Y$_{1-x}$Ca$_{x}$TiO$_{3}$

Authors: S. Hameed, I. Khayr, J. Joe, G. Q. Zhao, Y. Cai, K. M. Kojima, S. Chi, T. J. Williams, M. Matsuda, Y. J. Uemura, M. Greven

Abstract: Neutron scattering, magnetometry, and muon spin rotation ($μ$SR) measurements were performed to investigate the magnetic order and spin dynamics across the ferromagnet-to-paramagnet transition in the hole-doped Mott insulator Y$_{1-x}$Ca$_x$TiO$_3$. We find that the transition proceeds through a volume-wise phase separation into ferromagnetic and paramagnetic regions. Spin fluctuations with a char… ▽ More Neutron scattering, magnetometry, and muon spin rotation ($μ$SR) measurements were performed to investigate the magnetic order and spin dynamics across the ferromagnet-to-paramagnet transition in the hole-doped Mott insulator Y$_{1-x}$Ca$_x$TiO$_3$. We find that the transition proceeds through a volume-wise phase separation into ferromagnetic and paramagnetic regions. Spin fluctuations with a characteristic timescale of $\sim$ 0.1 $μ$s, as detected via $μ$SR, are observed to appear at Ca concentrations $x \geq 0.10$. The magnetic phase separation, accompanied by a modest dynamic response, represents a novel behavior in Mott systems near the loss of magnetic order. It is linked to a previously observed insulator-metal transition and the associated electronic phase separation into hole-poor Mott insulating and hole-rich metallic phases for $0 < x < 0.50$. In particular, the $x$-dependence of the paramagnetic volume fraction strongly correlates with that of the volume fraction of the hole-rich metallic phase. The spin-wave spectra reveal a doping-induced crossover from isotropic to two-dimensional anisotropic exchange interactions, reflecting substantial changes in the orbital state with increasing Ca content. △ Less

Submitted 17 February, 2025; originally announced February 2025.

Comments: 6 figures; supplement included

Vacancy-induced suppression of CDW order and its impact on magnetic order in kagome antiferromagnet FeGe

Authors: Mason L. Klemm, Saif Siddique, Yuan-Chun Chang, Sijie Xu, Yaofeng Xie, Tanner Legvold, Mehrdad T. Kiani, Feng Ye, Huibo Cao, Yiqing Hao, Wei Tian, Hubertus Luetkens, Masaaki Matsuda, Douglas Natelson, Zurab Guguchia, Chien-Lung Huang, Ming Yi, Judy J. Cha, Pengcheng Dai

Abstract: Two-dimensional (2D) kagome lattice metals are interesting because they display flat electronic bands, Dirac points, Van Hove singularities, and can have interplay between charge density wave (CDW), magnetic order, and superconductivity. In kagome lattice antiferromagnet FeGe, a short-range CDW order was found deep within an antiferromagnetically ordered state, interacting with the magnetic order.… ▽ More Two-dimensional (2D) kagome lattice metals are interesting because they display flat electronic bands, Dirac points, Van Hove singularities, and can have interplay between charge density wave (CDW), magnetic order, and superconductivity. In kagome lattice antiferromagnet FeGe, a short-range CDW order was found deep within an antiferromagnetically ordered state, interacting with the magnetic order. Surprisingly, post-growth annealing of FeGe at 560$^{\circ}$C can suppress the CDW order while annealing at 320$^{\circ}$C induces a long-range CDW order, with the ability to cycle between the states repeatedly by annealing. Here we perform transport, neutron scattering, scanning transmission electron microscopy (STEM), and muon spin rotation ($μ$SR) experiments to unveil the microscopic mechanism of the annealing process and its impact on magneto-transport, CDW, and magnetic properties of FeGe. We find that 560$^{\circ}$C annealing creates germanium vacancies uniformly distributed throughout the FeGe kagome lattice, which prevent the formation of Ge-Ge dimers necessary for the CDW order. Upon annealing at 320$^{\circ}$C, the system segregates into stoichiometric FeGe regions with long-range CDW order and regions with stacking faults that act as nucleation sites for the CDW. The presence or absence of CDW order greatly affects the anomalous Hall effect, incommensurate magnetic order, and spin-lattice coupling in FeGe, thus placing FeGe as the only known kagome lattice material with a tunable CDW and magnetic order, potentially useful for sensing and information transmission. △ Less

Submitted 17 October, 2024; originally announced October 2024.

Pulling order back from the brink of disorder: Observation of a nodal line spin liquid and fluctuation stabilized order in K$_2$IrCl$_6$

Authors: Qiaochu Wang, Alberto de la Torre, Jose A. Rodriguez-Rivera, Andrey A. Podlesnyak, Wei Tian, Adam A. Aczel, Masaaki Matsuda, Philip J. Ryan, Jong-Woo Kim, Jeffrey G. Rau, Kemp W. Plumb

Abstract: Competing interactions in frustrated magnets can give rise to highly degenerate ground states from which correlated liquid-like states of matter often emerge. The scaling of this degeneracy influences the ultimate ground state, with extensive degeneracies potentially yielding quantum spin liquids, while sub-extensive or smaller degeneracies yield static orders. A longstanding problem is to underst… ▽ More Competing interactions in frustrated magnets can give rise to highly degenerate ground states from which correlated liquid-like states of matter often emerge. The scaling of this degeneracy influences the ultimate ground state, with extensive degeneracies potentially yielding quantum spin liquids, while sub-extensive or smaller degeneracies yield static orders. A longstanding problem is to understand how ordered states precipitate from this degenerate manifold and what echoes of the degeneracy survive ordering. Here, we use neutron scattering to experimentally demonstrate a new "nodal line" spin liquid, where spins collectively fluctuate within a sub-extensive manifold spanning one-dimensional lines in reciprocal space. Realized in the spin-orbit coupled, face-centered cubic iridate K$_2$IrCl$_6$, we show that the sub-extensive degeneracy is robust, but remains susceptible to fluctuations or longer range interactions which cooperate to select a magnetic order at low temperatures. Proximity to the nodal line spin liquid influences the ordered state, enhancing the effects of quantum fluctuations and stabilizing it through the opening of a large spin-wave gap. Our results demonstrate quantum fluctuations can act counter-intuitively in frustrated materials: instead of destabilizing ordering, at the brink of the nodal spin liquid they can act to stabilize it and dictate its low-energy physics. △ Less

Submitted 24 July, 2024; originally announced July 2024.

Comments: Main article: 9 pages, 3 figures. Supplemental material: 22 pages, 15 figures

Journal ref: Phys. Rev. X 15, 021021 (2025)

Incipient nematicity from electron flat bands in a kagome metal

Authors: Nathan Drucker, Thanh Nguyen, Manasi Mandal, Phum Siriviboon, Yujie Quan, Artittaya Boonkird, Ryotaro Okabe, Fankang Li, Kaleb Buragge, Fumiaki Funuma, Masaaki Matsuda, Douglas Abernathy, Travis Williams, Songxue Chi, Feng Ye, Christie Nelson, Bolin Liao, Pavel Volkov, Mingda Li

Abstract: Engineering new quantum phases requires fine tuning of the electronic, orbital, spin, and lattice degrees of freedom. To this end, the kagome lattice with flat bands has garnered great attention by hosting various topological and correlated phases, when the flat band is at the Fermi level. Here we discover unconventional nematiciy in kagome metal CoSn, where flat bands are fully occupied below the… ▽ More Engineering new quantum phases requires fine tuning of the electronic, orbital, spin, and lattice degrees of freedom. To this end, the kagome lattice with flat bands has garnered great attention by hosting various topological and correlated phases, when the flat band is at the Fermi level. Here we discover unconventional nematiciy in kagome metal CoSn, where flat bands are fully occupied below the Fermi level. Thermodynamic, dilatometry, resonant X-ray scattering, inelastic neutron scattering, Larmor diffraction, and thermoelectric measurements consistently hint at rotational symmetry-breaking and nematic order that is pronounced only near T=225 K. These observations, principally the nematic's finite temperature stability -- incipience -- can be explained by a phenomenological model which reveals that thermally excited flat bands promote symmetry breaking at a characteristic temperature. Our work shows that thermal fluctuations, which are typically detrimental for correlated electron phases, can induce new ordered states of matter, avoiding the requirements for fine tuning of electronic bands. △ Less

Submitted 30 January, 2024; originally announced January 2024.

Comments: 37 pages, 5 main figures, 14 supplementary figures

Experimental Evidence for Non-spherical Magnetic Form Factor in Ru$^{3+}$

Authors: Colin L. Sarkis, John W. Villanova, Casey Eichstaedt, Adolfo G. Eguiluz, Jaime A. Fernandez-Baca, Masaaki Matsuda, Jiaqiang Yan, Christian Balz, Arnab Banerjee, D. Alan Tennant, Tom Berlijn, Stephen E. Nagler

Abstract: The Mott insulator $α$-RuCl$_3$ has generated great interest in the community due to its possible field-induced Kitaev quantum spin liquid state. Despite enormous effort spent trying to obtain the form of the low energy Hamiltonian, there is currently no agreed upon set of parameters which is able to explain all of the data. A key piece of missing information lies in the determination of the magne… ▽ More The Mott insulator $α$-RuCl$_3$ has generated great interest in the community due to its possible field-induced Kitaev quantum spin liquid state. Despite enormous effort spent trying to obtain the form of the low energy Hamiltonian, there is currently no agreed upon set of parameters which is able to explain all of the data. A key piece of missing information lies in the determination of the magnetic form factor of Ru$^{3+}$, particularly for a true quantitative treatment of inelastic neutron scattering data. Here we present the experimentally derived magnetic form factor of Ru$^{3+}$ in the low spin 4$d^5$ state using polarized neutron diffraction within the paramagnetic regime on high quality single crystals of $α$-RuCl$_3$. We observe strong evidence of an anisotropic form factor, expected of the spin-orbit coupled $j_{\textrm{eff}} = \frac{1}{2}$ ground state. We model the static magnetization density in increasing complexity from simple isotropic cases, to a multipolar expansion, and finally \emph{ab initio} calculations of the generalized $j_{\textrm{eff}} = \frac{1}{2}$ ground state. Comparison of both single ion models and inclusion of Cl$^-$ anions support the presence of hybridization of Ru$^{3+}$ with the surrounding Cl$^{-}$ ligands. △ Less

Submitted 31 October, 2023; originally announced November 2023.

Symmetry breaking and ascending in the magnetic kagome metal FeGe

Authors: Shangfei Wu, Mason Klemm, Jay Shah, Ethan T. Ritz, Chunruo Duan, Xiaokun Teng, Bin Gao, Feng Ye, Masaaki Matsuda, Fankang Li, Xianghan Xu, Ming Yi, Turan Birol, Pengcheng Dai, Girsh Blumberg

Abstract: Spontaneous symmetry breaking-the phenomenon where an infinitesimal perturbation can cause the system to break the underlying symmetry-is a cornerstone concept in the understanding of interacting solid-state systems. In a typical series of temperature-driven phase transitions, higher temperature phases are more symmetric due to the stabilizing effect of entropy that becomes dominant as the tempera… ▽ More Spontaneous symmetry breaking-the phenomenon where an infinitesimal perturbation can cause the system to break the underlying symmetry-is a cornerstone concept in the understanding of interacting solid-state systems. In a typical series of temperature-driven phase transitions, higher temperature phases are more symmetric due to the stabilizing effect of entropy that becomes dominant as the temperature is increased. However, the opposite is rare but possible when there are multiple degrees of freedom in the system. Here, we present such an example of a symmetry-ascending phenomenon in a magnetic kagome metal FeGe by utilizing neutron Larmor diffraction and Raman spectroscopy. In the paramagnetic state at 460K, we confirm that the crystal structure is indeed hexagonal kagome lattice. On cooling to TN, the crystal structure changes from hexagonal to monoclinic with in-plane lattice distortions on the order of 10^(-4) and the associated splitting of the double degenerate phonon mode of the pristine kagome lattice. Upon further cooling to TCDW, the kagome lattice shows a small negative thermal expansion, and the crystal structure becomes more symmetric gradually upon further cooling. Increasing the crystalline symmetry upon cooling is unusual, it originates from an extremely weak structural instability that coexists and competes with the CDW and magnetic orders. These observations are against the expectations for a simple model with a single order parameter, hence can only be explained by a Landau free energy expansion that takes into account multiple lattice, charge, and spin degrees of freedom. Thus, the determination of the crystalline lattice symmetry as well as the unusual spin-lattice coupling is a first step towards understanding the rich electronic and magnetic properties of the system and sheds new light on intertwined orders where the lattice degree of freedom is no longer dominant. △ Less

Submitted 8 March, 2024; v1 submitted 25 September, 2023; originally announced September 2023.

Comments: 20 pages with 10 figures, replaced with journal version

Journal ref: Phys. Rev. X 14, 011043 (2024)

Helical magnetic state in the vicinity of the pressure-induced superconducting phase in MnP

Authors: S. E. Dissanayake, M. Matsuda, K. Yoshimi, S. Kasamatsu, F. Ye, S. Chi, W. Steinhardt, G. Fabbris, S. Haravifard, J. -G. Cheng, J. -Q. Yan, J. Gouchi, Y. Uwatoko

Abstract: MnP is a metal that shows successive magnetic transitions from paramagnetic to ferromagnetic and helical magnetic phases at ambient pressure with decreasing temperature. With applied pressure, the magnetic transition temperatures decrease and superconductivity appears around 8 GPa where the magnetic order is fully suppressed and the quantum critical behavior is observed. These results suggest that… ▽ More MnP is a metal that shows successive magnetic transitions from paramagnetic to ferromagnetic and helical magnetic phases at ambient pressure with decreasing temperature. With applied pressure, the magnetic transition temperatures decrease and superconductivity appears around 8 GPa where the magnetic order is fully suppressed and the quantum critical behavior is observed. These results suggest that MnP is an unconventional superconductor in which magnetic fluctuations may be relevant to the superconducting pairing mechanism. In order to elucidate the magnetic ground state adjacent to the superconducting phase first discovered in Mn-based materials, high-pressure neutron diffraction measurements have been performed in hydrostatic pressure up to 7.5 GPa. The helical magnetic structure with the propagation vector along the $b$ axis, reported previously at 3.8 GPa, was found to be robust up to 7.5 GPa. First principles and classical Monte Carlo calculations have also been performed to understand how the pressure-driven magnetic phase transitions are coupled with change of the exchange interactions. The calculations, which qualitatively reproduce the magnetic structures as a function of pressure, suggest that the exchange interactions change drastically with applied pressure and the further-neighbor interactions become more influential at high pressures. Combining the experimental and theoretical results, we describe the detail of exchange interactions in the vicinity of the superconducting phase which is critical to understand the pairing mechanism of the unconventional superconductivity in MnP. △ Less

Submitted 25 August, 2023; originally announced August 2023.

Comments: 15 pages, 10 figures

Journal ref: Physical Review Research 5, 043026 (2023)

Short-range magnetic correlations in quasicrystalline i-Tb-Cd

Authors: P. Das, A. Kreyssig, G. S. Tucker, A. Podlesnyak, Feng Ye, Masaaki Matsuda, T. Kong, S. L. Bud'ko, P. C. Canfield, R. Flint, P. P. Orth, T. Yamada, R. J. McQueeney, A. I. Goldman

Abstract: We report on elastic and inelastic neutron scattering from single-grain isotopically-enriched samples to elucidate the local magnetic correlations between Tb$^{3+}$ moments in quasicrystalline i-Tb-Cd. The inelastic neutron scattering measurements of the CEF excitations demonstrated that the Tb$^{3+}$ moments are directed primarily along the local five-fold axes of the Tsai-type cluster as was fou… ▽ More We report on elastic and inelastic neutron scattering from single-grain isotopically-enriched samples to elucidate the local magnetic correlations between Tb$^{3+}$ moments in quasicrystalline i-Tb-Cd. The inelastic neutron scattering measurements of the CEF excitations demonstrated that the Tb$^{3+}$ moments are directed primarily along the local five-fold axes of the Tsai-type cluster as was found for the TbCd6 approximant phase. Based on the inelastic measurements, we consider of a simple Ising-type model for the moment configurations on a single Tb$^{3+}$ icosahedron and enumerate the lowest energy moment configurations. We then calculate the diffuse scattering from these configurations and compare with the experimental magnetic diffuse scattering measurements to identify the most likely single cluster moment configurations and find reasonable agreement between the broad features observed in our scattering simulations. We further consider the role of higher-order (longer range) intercluster correlations for the magnetic scattering. △ Less

Submitted 22 August, 2023; originally announced August 2023.

Journal ref: Phys. Rev. B 108, 134421 (2023)

Spin dynamics of the $E_8$ particles

Authors: Xiao Wang, Konrad Puzniak, Karin Schmalzl, C. Balz, M. Matsuda, Akira Okutani, M. Hagiwara, Jie Ma, Jianda Wu, Bella Lake

Abstract: In this article, we report on inelastic neutron scattering measurements on a quasi-1D antiferromagnet BaCo$_2$V$_2$O$_8$ under a transverse magnetic field applied along the (0,1,0) direction. Combining results of inelastic neutron scattering experiments, analytical analysis, and numerical simulations, we precisely studied the $E_8$ excitations appearing in the whole Brillouin zone at… ▽ More In this article, we report on inelastic neutron scattering measurements on a quasi-1D antiferromagnet BaCo$_2$V$_2$O$_8$ under a transverse magnetic field applied along the (0,1,0) direction. Combining results of inelastic neutron scattering experiments, analytical analysis, and numerical simulations, we precisely studied the $E_8$ excitations appearing in the whole Brillouin zone at $B_c^{1D}\approx 4.7$ T. The energy scan at $Q=(0,0,2)$ reveals a match between the data and the theoretical prediction of energies of multiple $E_8$ excitations. Furthermore, dispersions of the lightest three $E_8$ particles have been clearly observed, confirming the existence of the $E_8$ particles in BaCo$_2$V$_2$O$_8$. Our results lay down a concrete ground to systematically study the physics of the exotic $E_8$ particles. △ Less

Submitted 31 July, 2023; originally announced August 2023.

Comments: 10 pages, 4 figures

Journal ref: Science Bulletin (2024)

Fermi surface reconstruction due to the orthorhombic distortion in Dirac semimetal YbMnSb$_2$

Authors: Dilip Bhoi, Feng Ye, Hanming Ma, Xiaoling Shen, Arvind Maurya, Shusuke Kasamatsu, Takahiro Misawa, Kazuyoshi Yoshimi, Taro Nakajima, Masaaki Matsuda, Yoshiya Uwatoko

Abstract: Dirac semi-metal with magnetic atoms as constituents delivers an interesting platform to investigate the interplay of Fermi surface (FS) topology, electron correlation, and magnetism. One such family of semi-metal is YbMn$Pn_2$ ($Pn$ = Sb, Bi), which is being actively studied due to the intertwined spin and charge degrees of freedom. In this Letter, we investigate the relationship between the magn… ▽ More Dirac semi-metal with magnetic atoms as constituents delivers an interesting platform to investigate the interplay of Fermi surface (FS) topology, electron correlation, and magnetism. One such family of semi-metal is YbMn$Pn_2$ ($Pn$ = Sb, Bi), which is being actively studied due to the intertwined spin and charge degrees of freedom. In this Letter, we investigate the relationship between the magnetic/crystal structures and FS topology of YbMnSb$_2$ using single crystal x-ray diffraction, neutron scattering, magnetic susceptibility, magnetotransport measurement and complimentary DFT calculation. Contrary to previous reports, the x-ray and neutron diffraction reveal that YbMnSb$_2$ crystallizes in an orthorhombic $Pnma$ structure with notable anti-phase displacement of the magnetic Mn ions that increases in magnitude upon cooling. First principles DFT calculation reveals a reduced Brillouin zone and more anisotropic FS of YbMnSb$_2$ compared to YbMnBi$_2$ as a result of the orthorhombicity. Moreover, the hole type carrier density drops by two orders of magnitude as YbMnSb$_2$ orders antiferromagnetically indicating band folding in magnetic ordered state. In addition, the Landau level fan diagram yields a non-trivial nature of the SdH quantum oscillation frequency arising from the Dirac-like Fermi pocket. These results imply that YbMnSb$_2$ is an ideal platform to explore the interplay of subtle lattice distortion, magnetic order, and topological transport arising from relativistic quasiparticles. △ Less

Submitted 22 June, 2023; originally announced June 2023.

Comments: 11 pages, contains 4 figures and 7 Supplemental Figures

Static and dynamical properties of the spin-5/2 nearly ideal triangular lattice antiferromagnet Ba3MnSb2O9

Authors: Mingfang Shu, Weicen Dong, Jinlong Jiao, Jiangtao Wu, Gaoting lin, Tao Hong, Huibo Cao, Masaaki Matsuda, Wei Tian, Songxue Chi, Georg Ehlers, Zhongwen Ouyang, Hongwei Chen, Youming Zou, Zhe Qu, Qing Huang, Haidong Zhou, Yoshitomo Kamiya, Jie Ma

Abstract: We study the ground state and spin excitations in Ba3MnSb2O9, an easy-plane S = 5/2 triangular lattice antiferromagnet. By combining single-crystal neutron scattering, electric spin resonance (ESR), and spin wave calculations, we determine the frustrated quasi-two-dimensional spin Hamiltonian parameters describing the material. While the material has a slight monoclinic structural distortion, whic… ▽ More We study the ground state and spin excitations in Ba3MnSb2O9, an easy-plane S = 5/2 triangular lattice antiferromagnet. By combining single-crystal neutron scattering, electric spin resonance (ESR), and spin wave calculations, we determine the frustrated quasi-two-dimensional spin Hamiltonian parameters describing the material. While the material has a slight monoclinic structural distortion, which could allow for isosceles-triangular exchanges and biaxial anisotropy by symmetry, we observe no deviation from the behavior expected for spin waves in the in-plane 120o state. Even the easy-plane anisotropy is so small that it can only be detected by ESR in our study. In conjunction with the quasi-two-dimensionality, our study establishes that Ba3MnSb2O9 is a nearly ideal triangular lattice antiferromagnet with the quasi-classical spin S = 5/2, which suggests that it has the potential for an experimental study of Z- or Z2-vortex excitations. △ Less

Submitted 7 September, 2023; v1 submitted 9 June, 2023; originally announced June 2023.

Effect of random antiferromagnetic exchange on the spin waves in a three-dimensional Heisenberg ferromagnet

Authors: S. Hameed, Z. Wang, D. M. Gautreau, J. Joe, K. P. Olson, S. Chi, P. M. Gehring, T. Hong, D. M. Pajerowski, T. J. Williams, Z. Xu, M. Matsuda, T. Birol, R. M. Fernandes, M. Greven

Abstract: Neutron scattering is used to study spin waves in the three-dimensional Heisenberg ferromagnet YTiO$_3$, with spin-spin exchange disorder introduced $via$ La-substitution at the Y site. No significant changes are observed in the spin-wave dispersion up to a La concentration of 20%. However, a strong broadening of the spectrum is found, indicative of shortened spin-wave lifetimes. Density-functiona… ▽ More Neutron scattering is used to study spin waves in the three-dimensional Heisenberg ferromagnet YTiO$_3$, with spin-spin exchange disorder introduced $via$ La-substitution at the Y site. No significant changes are observed in the spin-wave dispersion up to a La concentration of 20%. However, a strong broadening of the spectrum is found, indicative of shortened spin-wave lifetimes. Density-functional theory calculations predict minimal changes in exchange constants as a result of average structural changes due to La substitution, in agreement with the data. The absence of significant changes in the spin-wave dispersion, the considerable lifetime effect, and the reduced ordered magnetic moment previously observed in the La-substituted system are qualitatively captured by an isotropic, nearest-neighbor, three-dimensional Heisenberg ferromagnet model with random antiferromagnetic exchange. We therefore establish Y$_{1-x}$La$_x$TiO$_3$ as a model system to study the effect of antiferromagnetic spin-exchange disorder in a three-dimensional Heisenberg ferromagnet. △ Less

Submitted 7 May, 2023; originally announced May 2023.

Comments: 6 pages and 5 figures in main text. Supplementary material included

Journal ref: Phys. Rev. B 108, 134406 (2023)

Large anomalous Hall effect and unusual domain switching in an orthorhombic antiferromagnetic material NbMnP

Authors: Hisashi Kotegawa, Yoshiki Kuwata, Vu Thi Ngoc Huyen, Yuki Arai, Hideki Tou, Masaaki Matsuda, Keiki Takeda, Hitoshi Sugawara, Michi-To Suzuki

Abstract: Specific antiferromagnetic (AF) spin configurations generate large anomalous Hall effects (AHEs) even at zero magnetic field through nonvanishing Berry curvature in momentum space. In addition to restrictions on AF structures, suitable control of AF domains is essential to observe this effect without cancellations among its domains; therefore, compatible materials remain limited. Here we show that… ▽ More Specific antiferromagnetic (AF) spin configurations generate large anomalous Hall effects (AHEs) even at zero magnetic field through nonvanishing Berry curvature in momentum space. In addition to restrictions on AF structures, suitable control of AF domains is essential to observe this effect without cancellations among its domains; therefore, compatible materials remain limited. Here we show that an orthorhombic noncollinear AF material, NbMnP, acquired AF structure-based AHE and controllability of the AF domains. Theoretical calculations indicated that a large Hall conductivity of $\sim230$ $Ω^{-1}$cm$^{-1}$ originated from the AF structure of NbMnP. Symmetry considerations explained the production of a small net magnetization, whose anisotropy enabled the generation and cancellation of the Hall responses using magnetic fields in different directions. Finally, asymmetric hysteresis in NbMnP shows potential for development of controllability of responses in AF materials. △ Less

Submitted 18 October, 2023; v1 submitted 3 May, 2023; originally announced May 2023.

Comments: 13 pages, 7 figures, including supplementary information

Journal ref: npj Quantum Materials 8, 56 (2023)

Lattice Instability of UTe$_2$ Studied by Ultrasonic Measurements

Authors: Keita Ushida, Tatsuya Yanagisawa, Ruo Hibino, Masato Matsuda, Hiroyuki Hidaka, Hiroshi Amitsuka, Georg Knebel, Jacques Flouquet, Dai Aoki

Abstract: The elastic constants of an unconventional superconductor, UTe$_2$, were investigated using ultrasound. In this paper, we report the elastic response of the normal state at temperatures down to 2 K and up to 14 T for $H \parallel b$ at ambient pressure. The transverse ultrasonic mode $C_{55}$, which corresponds to the strain susceptibility of $\varepsilon_{zx}$, shows softening with decreasing tem… ▽ More The elastic constants of an unconventional superconductor, UTe$_2$, were investigated using ultrasound. In this paper, we report the elastic response of the normal state at temperatures down to 2 K and up to 14 T for $H \parallel b$ at ambient pressure. The transverse ultrasonic mode $C_{55}$, which corresponds to the strain susceptibility of $\varepsilon_{zx}$, shows softening with decreasing temperature, whereas the $C_{44}$ and $C_{33}$ modes do not show such softening. This clear mode dependence strongly suggests that UTe$_2$ has a lattice instability for this specific symmetry. △ Less

Submitted 12 November, 2022; originally announced November 2022.

Comments: Proceedings of 29th International Conference on LOW TEMPERATURE PHYSICS

Journal ref: JPS Conf. Proc. 38 (2023) 011021

Magnetic Structure and Spin Fluctuations in Colossal Magnetoresistance Ferrimagnet Mn3Si2Te6

Authors: Feng Ye, Masaaki Matsuda, Zachary Morgan, Todd Sherline, Yifei Ni, Hengdi Zhao, G. Cao

Abstract: The ferrimagnetic insulator Mn3Si2Te6, which features a Curie temperature Tc at 78 K and a delicate yet consequential magnetic frustration, exhibits colossal magnetoresistance (CMR) when the magnetic field is applied along the magnetic hard axis, surprisingly inconsistent with existing precedents [Y. Ni, H. Zhao, Y. Zhang et al. Phys. Rev. B 103, L161105 (2021)]. This discovery motivates a thoroug… ▽ More The ferrimagnetic insulator Mn3Si2Te6, which features a Curie temperature Tc at 78 K and a delicate yet consequential magnetic frustration, exhibits colossal magnetoresistance (CMR) when the magnetic field is applied along the magnetic hard axis, surprisingly inconsistent with existing precedents [Y. Ni, H. Zhao, Y. Zhang et al. Phys. Rev. B 103, L161105 (2021)]. This discovery motivates a thorough single-crystal neutron diffraction study in order to gain insights into the magnetic structure and its hidden correlation with the new type of CMR. Here we report a noncollinear magnetic structure below the Tc where the moments lie predominantly within the basal plane but tilt toward the c axis by ~10o at ambient conditions. A substantial magnetic diffuse scattering decays slowly and persists well above the Tc. The evolution of the spin correlation lengths agrees well with the electrical resistivity, underscoring the role of spin fluctuation contributing to the magnetoresistivity near the transition. Application of magnetic field along the c axis, renders a swift occurrence of CMR but only a slow tilting of the magnetic moments toward the c axis. The unparalleled changes indicate a non-consequential role of magnetic polarization. △ Less

Submitted 1 November, 2022; v1 submitted 27 September, 2022; originally announced September 2022.

Comments: 4 Figures

Journal ref: Phys. Rev. B 106 L180402 (2022)

Pressure dependence of the magnetic ground state in CePtSi2

Authors: S. E. Dissanayake, F. Ye, W. Tian, M. Matsuda, H. Muto, S. Suzuki, T. Nakano, S. Watanabe, J. Gouchi, Y. Uwatoko

Abstract: CePtSi2 was reported to exhibit an antiferromagnetic order below T*=1.8 K at ambient pressure, a valence state change at ~1.2 GPa, and superconductivity in the range between 1.4 and 2.1 GPa with the maximum transition temperature of 0.14 K [T. Nakano et al., Phys. Rev. B 79, 172507 (2009)]. We have performed polycrystalline and single crystal neutron diffraction experiments to determine the magnet… ▽ More CePtSi2 was reported to exhibit an antiferromagnetic order below T*=1.8 K at ambient pressure, a valence state change at ~1.2 GPa, and superconductivity in the range between 1.4 and 2.1 GPa with the maximum transition temperature of 0.14 K [T. Nakano et al., Phys. Rev. B 79, 172507 (2009)]. We have performed polycrystalline and single crystal neutron diffraction experiments to determine the magnetic structure under ambient and high pressures. We found that incommensurate magnetic peaks with the magnetic propagation vector of (0.32, 0, 0.11) at ambient pressure below T_{SDW}~1.25 K. Those magnetic peaks which originate from a spin-density-wave order with the easy axis along the c axis and an averaged ordered moment of 0.45(5) mu_B, suggesting that there may be an intermediate phase between T* and T_{SDW}. Applying pressures, the magnetic propagation vector shows no change and the magnetic order disappears around 1.0 GPa, which is much lower than the critical pressure for the superconducting phase. The results suggest that other than magnetic fluctuations may play a primary role in the superconducting pairing mechanism. △ Less

Submitted 16 June, 2022; originally announced June 2022.

Comments: 6 pages, 6 figures

Journal ref: Physical Review B 105, 245111 (2022)

Strongly-overdoped La$_{2-x}$Sr$_x$CuO$_4$: Evidence for Josephson-coupled grains of strongly-correlated superconductor

Authors: Yangmu Li, A. Sapkota, P. M. Lozano, Zengyi Du, Hui Li, Zebin Wu, Asish K. Kundu, R. J. Koch, Lijun Wu, B. L. Winn, Songxue Chi, M. Matsuda, M. Frontzek, E. S. Bozin, Yimei Zhu, I. Bozovic, Abhay N. Pasupathy, Ilya K. Drozdov, Kazuhiro Fujita, G. D. Gu, Igor Zaliznyak, Qiang Li, J. M. Tranquada

Abstract: The interpretation of how superconductivity disappears in cuprates at large hole doping has been controversial. To address this issue, we present an experimental study of single-crystal and thin film samples of La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) with $x\ge0.25$. In particular, measurements of bulk susceptibility on LSCO crystals with $x=0.25$ indicate an onset of diamagnetism at $T_{c1}=38.5$ K, with… ▽ More The interpretation of how superconductivity disappears in cuprates at large hole doping has been controversial. To address this issue, we present an experimental study of single-crystal and thin film samples of La$_{2-x}$Sr$_x$CuO$_4$ (LSCO) with $x\ge0.25$. In particular, measurements of bulk susceptibility on LSCO crystals with $x=0.25$ indicate an onset of diamagnetism at $T_{c1}=38.5$ K, with a sharp transition to a phase with full bulk shielding at $T_{c2}=18$ K, independent of field direction. Strikingly, the in-plane resistivity only goes to zero at $T_{c2}$. Inelastic neutron scattering on $x=0.25$ crystals confirms the presence of low-energy incommensurate magnetic excitations with reduced strength compared to lower doping levels. The ratio of the spin gap to $T_{c2}$ is anomalously large. Our results are consistent with a theoretical prediction for strongly overdoped cuprates by Spivak, Oreto, and Kivelson, in which superconductivity initially develops within disconnected self-organized grains characterized by a reduced hole concentration, with bulk superconductivity occurring only after superconductivity is induced by proximity effect in the surrounding medium of higher hole concentration. Beyond the superconducting-to-metal transition, local differential conductance measurements on an LSCO thin film suggest that regions with pairing correlations survive, but are too dilute to support superconducting order. Future experiments will be needed to test the degree to which these results apply to overdoped cuprates in general. △ Less

Submitted 21 December, 2022; v1 submitted 3 May, 2022; originally announced May 2022.

Comments: 21 pages, 15 figures; added more sample characterizations, results for another sample, more discussion; accepted version

Journal ref: Phys. Rev. B 106, 224515 (2022)

Hidden local symmetry breaking in a kagome-lattice magnetic Weyl semimetal

Authors: Qiang Zhang, Yuanpeng Zhang, Masaaki Matsuda, Vasile O Garlea, Jiaqiang Yan, Michael A. McGuire, D. Alan Tennant, Satoshi Okamoto

Abstract: Exploring the relationship between intriguing physical properties and structural complexity is a central topic in studying modern functional materials. Co$_{3}$Sn$_{2}$S$_{2}$, a new discovered kagome-lattice magnetic Weyl semimetal, has triggered intense interest owing to the intimate coupling between topological semimetallic states and peculiar magnetic properties. However, the origins of the ma… ▽ More Exploring the relationship between intriguing physical properties and structural complexity is a central topic in studying modern functional materials. Co$_{3}$Sn$_{2}$S$_{2}$, a new discovered kagome-lattice magnetic Weyl semimetal, has triggered intense interest owing to the intimate coupling between topological semimetallic states and peculiar magnetic properties. However, the origins of the magnetic phase separation and spin glass state below $T_{C}$ in this ordered compound are two unresolved yet important puzzles in understanding its magnetism. Here, we report the discovery of local symmetry breaking surprisingly co-emerges with the onset of ferromagnetic order in Co$_{3}$Sn$_{2}$S$_{2}$, by a combined use of neutron total scattering and half polarized neutron diffraction. The mismatch of local and average symmetries occurs below $T_{C}$, indicating that Co$_{3}$Sn$_{2}$S$_{2}$ evolves to an intrinsically lattice disordered system when the ferromagnetic order is established. The local symmetry breaking with intrinsic lattice disorder provides new understandings to the puzzling magnetic properties. Our density function theory calculation indicates that the local symmetry breaking is expected to reorient local ferromagnetic moments, unveiling the existence of the ferromagnetic instability associated with the lattice instability. Furthermore, DFT calculation unveils that the local symmetry breaking could affect the Weyl property by breaking mirror plane. Our findings highlight the fundamentally important role that the local symmetry breaking plays in advancing our understanding on the magnetic and topological properties in Co$_{3}$Sn$_{2}$S$_{2}$, which may draw the attention to explore the overlooked local symmetry breaking in Co$_{3}$Sn$_{2}$S$_{2}$, its derivatives, and more broadly in other topological Dirac/Weyl semimetals and kagome-lattice magnets. △ Less

Submitted 29 July, 2022; v1 submitted 16 February, 2022; originally announced February 2022.

Comments: 35 pages, 6 figures, 1 table, 1 Supplementary Information

Journal ref: J. Am. Chem. Soc. Published, 2022

Unsupervised learning-based structural analysis: Search for a characteristic low-dimensional space by local structures in atomistic simulations

Authors: Ryo Tamura, Momo Matsuda, Jianbo Lin, Yasunori Futamura, Tetsuya Sakurai, Tsuyoshi Miyazaki

Abstract: Owing to the advances in computational techniques and the increase in computational power, atomistic simulations of materials can simulate large systems with higher accuracy. Complex phenomena can be observed in such state-of-the-art atomistic simulations. However, it has become increasingly difficult to understand what is actually happening and mechanisms, for example, in molecular dynamics (MD)… ▽ More Owing to the advances in computational techniques and the increase in computational power, atomistic simulations of materials can simulate large systems with higher accuracy. Complex phenomena can be observed in such state-of-the-art atomistic simulations. However, it has become increasingly difficult to understand what is actually happening and mechanisms, for example, in molecular dynamics (MD) simulations. We propose an unsupervised machine learning method to analyze the local structure around a target atom. The proposed method, which uses the two-step locality preserving projections (TS-LPP), can find a low-dimensional space wherein the distributions of datapoints for each atom or groups of atoms can be properly captured. We demonstrate that the method is effective for analyzing the MD simulations of crystalline, liquid, and amorphous states and the melt-quench process from the perspective of local structures. The proposed method is demonstrated on a silicon single-component system, a silicon-germanium binary system, and a copper single-component system. △ Less

Submitted 29 July, 2021; originally announced July 2021.

Comments: 16 pages, 13 figures

Growth and characterization of large (Y,La)TiO$_3$ and (Y,Ca)TiO$_3$ single crystals

Authors: S. Hameed, J. Joe, L. R. Thoutam, J. Garcia-Barriocanal, B. Yu, G. Yu, S. Chi, T. Hong, T. J. Williams, J. W. Freeland, P. M. Gehring, Z. Xu, M. Matsuda, B. Jalan, M. Greven

Abstract: The Mott-insulating rare-earth titanates (RTiO$_3$, R being a rare-earth ion) are an important class of materials that encompasses interesting spin-orbital phases as well as ferromagnet-antiferromagnet and insulator-metal transitions. The growth of these materials has been plagued by difficulties related to overoxidation, which arises from a strong tendency of Ti$^{3+}$ to oxidize to Ti$^{4+}$. We… ▽ More The Mott-insulating rare-earth titanates (RTiO$_3$, R being a rare-earth ion) are an important class of materials that encompasses interesting spin-orbital phases as well as ferromagnet-antiferromagnet and insulator-metal transitions. The growth of these materials has been plagued by difficulties related to overoxidation, which arises from a strong tendency of Ti$^{3+}$ to oxidize to Ti$^{4+}$. We describe our efforts to grow sizable single crystals of YTiO$_3$ and its La-substituted and Ca-doped variants with the optical travelling-solvent floating-zone technique. We present sample characterization $via$ chemical composition analysis, magnetometry, charge transport, neutron scattering, x-ray absorption spectroscopy and x-ray magnetic circular dichroism to understand macroscopic physical property variations associated with overoxidation. Furthermore, we demonstrate a good signal-to-noise ratio in inelastic magnetic neutron scattering measurements of spin-wave excitations. A superconducting impurity phase, found to appear in Ca-doped samples at high doping levels, is identified as TiO. △ Less

Submitted 18 June, 2021; originally announced June 2021.

Journal ref: Phys. Rev. Materials 5, 125003 (2021)

Nature of the ferromagnetic-antiferromagnetic transition in Y$_{1-x}$La$_{x}$TiO$_{3}$

Authors: S. Hameed, S. El-Khatib, K. P. Olson, B. Yu, T. J. Williams, T. Hong, Q. Sheng, K. Yamakawa, J. Zang, Y. J. Uemura, G. Q. Zhao, C. Q. Jin, L. Fu, Y. Gu, F. Ning, Y. Cai, K. M. Kojima, J. W. Freeland, M. Matsuda, C. Leighton, M. Greven

Abstract: We explore the magnetically-ordered ground state of the isovalently-substituted Mott-insulator Y$_{1-x}$La$_{x}$TiO$_{3}$ for $x$ $\leq$ 0.3 via single crystal growth, magnetometry, neutron diffraction, x-ray magnetic circular dichroism (XMCD), muon spin rotation ($μ$SR) and small-angle neutron scattering (SANS). We find that the decrease in the magnetic transition temperature on approaching the f… ▽ More We explore the magnetically-ordered ground state of the isovalently-substituted Mott-insulator Y$_{1-x}$La$_{x}$TiO$_{3}$ for $x$ $\leq$ 0.3 via single crystal growth, magnetometry, neutron diffraction, x-ray magnetic circular dichroism (XMCD), muon spin rotation ($μ$SR) and small-angle neutron scattering (SANS). We find that the decrease in the magnetic transition temperature on approaching the ferromagnetic (FM) - antiferromagnetic (AFM) phase boundary at the La concentration $x_c$ $\approx$ 0.3 is accompanied by a strong suppression of both bulk and local ordered magnetic moments, along with a volume-wise separation into magnetically-ordered and paramagnetic regions. The thermal phase transition does not show conventional second-order behavior, since neither a clear signature of dynamic critical behavior nor a power-law divergence of the magnetic correlation length is found for the studied substitution range; this finding becomes increasingly obvious with substitution. Finally, from SANS and magnetometry measurements, we discern a crossover from easy-axis to easy-plane magneto-crystalline anisotropy with increasing La substitution. These results indicate complex changes in magnetic structure upon approaching the phase boundary. △ Less

Submitted 15 March, 2021; originally announced March 2021.

Comments: 16 pages, 16 figures

Journal ref: Phys. Rev. B 104, 024410 (2021)

Isotropic parallel antiferromagnetism in the magnetic-field-induced charge-ordered state of SmRu$_4$P$_{12}$ caused by $p$-$f$ hybridization

Authors: T. Matsumura, S. Michimura, T. Inami, C. H. Lee, M. Matsuda, H. Nakao, M. Mizumaki, N. Kawamura, M. Tsukagoshi, S. Tsutsui, H. Sugawara, K. Fushiya, T. D. Matsuda, R. Higashinaka, Y. Aoki

Abstract: Nature of the field-induced charge ordered phase (phase II) of SmRu$_4$P$_{12}$ has been investigated by resonant x-ray diffraction (RXD) and polarized neutron diffraction (PND), focusing on the relationship between the atomic displacements and the antiferromagnetic (AFM) moments of Sm. From the analysis of the interference between the non-resonant Thomson scattering and the resonant magnetic scat… ▽ More Nature of the field-induced charge ordered phase (phase II) of SmRu$_4$P$_{12}$ has been investigated by resonant x-ray diffraction (RXD) and polarized neutron diffraction (PND), focusing on the relationship between the atomic displacements and the antiferromagnetic (AFM) moments of Sm. From the analysis of the interference between the non-resonant Thomson scattering and the resonant magnetic scattering, combined with the spectral function obtained from x-ray magnetic circular dichroism, it is shown that the AFM moment of Sm prefers to be parallel to the field ($m_{\text{AF}} \parallel H$), giving rise to large and small moment sites around which the P$_{12}$ and Ru cage contract and expand, respectively. This is associated with the formation of the staggered ordering of the $Γ_7$-like and $Γ_8$-like crystal-field states, providing a strong piece of evidence for the charge order. PND was also performed to obtain complementary and unambiguous conclusion. In addition, isotropic and continuous nature of the phase II is demonstrated by the field-direction invariance of the interference spectrum in RXD. Crucial role of the $p$-$f$ hybridization is shown by resonant soft x-ray diffraction at the P $K$-edge ($1s\leftrightarrow 3p$), where we detected a resonance due to the spin polarized $3p$ orbitals reflecting the AFM order of Sm. △ Less

Submitted 29 December, 2020; originally announced December 2020.

Comments: 12 pages, 11 figures, supplemental material (5 pages, 9 figures), accepted for publication in Phys. Rev. B

Journal ref: Phys. Rev. B 102, 214444 (2020)

Complex magnetic phases in polar tetragonal intermetallic NdCoGe$_3$

Authors: Binod K. Rai, Ganesh Pokharel, Hasitha Suriya Arachchige, Seung-Hwan Do, Qiang Zhang, Masaaki Matsuda, Matthias Frontzek, Gabriele Sala, V. Ovidiu Garlea, Andrew D. Christianson, Andrew F. May

Abstract: Polar materials can host a variety of topologically significant magnetic phases, which often emerge from a modulated magnetic ground state. Relatively few noncentrosymmetric tetragonal materials have been shown to host topological spin textures and new candidate materials are necessary to expand the current theoretical models. This manuscript reports on the anisotropic magnetism in the polar, tetr… ▽ More Polar materials can host a variety of topologically significant magnetic phases, which often emerge from a modulated magnetic ground state. Relatively few noncentrosymmetric tetragonal materials have been shown to host topological spin textures and new candidate materials are necessary to expand the current theoretical models. This manuscript reports on the anisotropic magnetism in the polar, tetragonal material NdCoGe$_3$ via thermodynamic and neutron diffraction measurements. The previously reported $H$-$T$ phase diagram is updated to include several additional phases, which exist for both $H$ = 0 and with an applied field H$\perp$ c. Neutron diffraction data reveal that the magnetic structures below $T_{N1}$ = 3.70 K and $T_{N2}$ = 3.50 K are incommensurate, with a ground state magnetic order that is incommensurate in all directions with the propagation vector $\vec{k}$ = (0.494, 0.0044, 0.385) at 1.8 K. A unique magnetic structure solution is not achievable, but the possible single and multi-$\vec{k}$ spin models are discussed. These results demonstrate that NdCoGe3 hosts complicated magnetic order derived from modulated magnetic moments. △ Less

Submitted 18 December, 2020; originally announced December 2020.

Comments: 11 pages, 10 figures

Journal ref: Phys. Rev. B 103, 014426 (2021)

Evidence for pressure induced unconventional quantum criticality in the coupled spin ladder antiferromagnet C$_9$H$_{18}$N$_2$CuBr$_4$

Authors: Tao Hong, Tao Ying, Qing Huang, Sachith E. Dissanayake, Yiming Qiu, Mark M. Turnbull, Andrey A. Podlesnyak, Yan Wu, Huibo Cao, Yaohua Liu, Izuru Umehara, Jun Gouchi, Yoshiya Uwatoko, Masaaki Matsuda, David A. Tennant, Gia-Wei Chern, Kai P. Schmidt, Stefan Wessel

Abstract: Quantum phase transitions in quantum matter occur at zero temperature between distinct ground states by tuning a nonthermal control parameter. Often, they can be accurately described within the Landau theory of phase transitions, similarly to conventional thermal phase transitions. However, this picture can break down under certain circumstances. Here, we present a comprehensive study of the effec… ▽ More Quantum phase transitions in quantum matter occur at zero temperature between distinct ground states by tuning a nonthermal control parameter. Often, they can be accurately described within the Landau theory of phase transitions, similarly to conventional thermal phase transitions. However, this picture can break down under certain circumstances. Here, we present a comprehensive study of the effect of hydrostatic pressure on the magnetic structure and spin dynamics of the spin-1/2 ladder compound C$_9$H$_{18}$N$_2$CuBr$_4$. Single-crystal heat capacity and neutron diffraction measurements reveal that the N$\rm \acute{e}$el-ordered phase breaks down beyond a critical pressure of $P_{\rm c}$$\sim$1.0 GPa through a continuous quantum phase transition. Estimates of the critical exponents suggest that this transition may fall outside the traditional Landau paradigm. The inelastic neutron scattering spectra at 1.3 GPa are characterized by two well-separated gapped modes, including one continuum-like and another resolution-limited excitation in distinct scattering channels, which further indicates an exotic quantum-disordered phase above $P_{\rm c}$. △ Less

Submitted 19 May, 2022; v1 submitted 9 November, 2020; originally announced November 2020.

Comments: The revised version includes 10 pages and 5 figures in the main text. To appear in Nature Communications. Any comments are welcome

Journal ref: Nat. Commun. 13, 3073 (2022)

Formation of short-range magnetic order and avoided ferromagnetic quantum criticality in pressurized LaCrGe$_3$

Authors: Elena Gati, John M. Wilde, Rustem Khasanov, Li Xiang, Sachith Dissanayake, Ritu Gupta, Masaaki Matsuda, Feng Ye, Bianca Haberl, Udhara Kaluarachchi, Robert J. McQueeney, Andreas Kreyssig, Sergey L. Bud'ko, Paul C. Canfield

Abstract: LaCrGe$_3$ has attracted attention as a paradigm example of the avoidance of ferromagnetic (FM) quantum criticality in an itinerant magnet. By combining thermodynamic, transport, x-ray and neutron scattering as well as $μ$SR measurements, we refined the temperature-pressure phase diagram of LaCrGe$_3$. We provide thermodynamic evidence (i) for the first-order character of the FM transition when it… ▽ More LaCrGe$_3$ has attracted attention as a paradigm example of the avoidance of ferromagnetic (FM) quantum criticality in an itinerant magnet. By combining thermodynamic, transport, x-ray and neutron scattering as well as $μ$SR measurements, we refined the temperature-pressure phase diagram of LaCrGe$_3$. We provide thermodynamic evidence (i) for the first-order character of the FM transition when it is suppressed to low temperatures and (ii) for the formation of new phases at high pressures. From our microscopic data, we infer that short-range FM ordered clusters exist in these high-pressure phases. These results suggest that LaCrGe$_3$ is a rare example, which fills the gap between the two extreme limits of avoided FM quantum criticality in clean and strongly disordered metals. △ Less

Submitted 9 November, 2020; originally announced November 2020.

Comments: 7 pages, 4 figures plus Supplemental Information

Journal ref: Phys. Rev. B 103, 075111 (2021)

$\mathbf{q}=\mathbf{0}$ long-range magnetic order in centennialite CaCu$_3$(OD)$_6$Cl$_2$$\cdot$0.6D$_2$O: A spin-1/2 perfect kagome antiferromagnet with $J_1$-$J_2$-$J_d$

Authors: K. Iida, H. K. Yoshida, A. Nakao, H. O. Jeschke, Y. Iqbal, K. Nakajima, S. Ohira-Kawamura, K. Munakata, Y. Inamura, N. Murai, M. Ishikado, R. Kumai, T. Okada, M. Oda, K. Kakurai, M. Matsuda

Abstract: Crystal and magnetic structures of the mineral centennialite CaCu$_3$(OH)$_6$Cl$_2\cdot0.6$H$_2$O are investigated by means of synchrotron x-ray diffraction and neutron diffraction measurements complemented by density functional theory (DFT) and pseudofermion functional renormalization group (PFFRG) calculations. CaCu$_3$(OH)$_6$Cl$_2\cdot0.6$H$_2$O crystallizes in the $P\bar{3}m1$ space group and… ▽ More Crystal and magnetic structures of the mineral centennialite CaCu$_3$(OH)$_6$Cl$_2\cdot0.6$H$_2$O are investigated by means of synchrotron x-ray diffraction and neutron diffraction measurements complemented by density functional theory (DFT) and pseudofermion functional renormalization group (PFFRG) calculations. CaCu$_3$(OH)$_6$Cl$_2\cdot0.6$H$_2$O crystallizes in the $P\bar{3}m1$ space group and Cu$^{2+}$ ions form a geometrically perfect kagome network with antiferromagnetic $J_1$. No intersite disorder between Cu$^{2+}$ and Ca$^{2+}$ ions is detected. CaCu$_3$(OH)$_6$Cl$_2\cdot0.6$H$_2$O enters a magnetic long-range ordered state below $T_\text{N}=7.2$~K, and the $\mathbf{q}=\mathbf{0}$ magnetic structure with negative vector spin chirality is obtained. The ordered moment at 0.3~K is suppressed to $0.58(2)μ_\text{B}$. Our DFT calculations indicate the presence of antiferromagnetic $J_2$ and ferromagnetic $J_d$ superexchange couplings of a strength which places the system at the crossroads of three magnetic orders (at the classical level) and a spin-$\frac{1}{2}$ PFFRG analysis shows a dominance of $\mathbf{q}=\mathbf{0}$ type magnetic correlations, consistent with and indicating proximity to the observed $\mathbf{q}=\mathbf{0}$ spin structure. The results suggest that this material is located close to a quantum critical point and is a good realization of a $J_1$-$J_2$-$J_d$ kagome antiferromagnet. △ Less

Submitted 22 June, 2020; originally announced June 2020.

Comments: 4 figures and supplemental materials

Journal ref: Phys. Rev. B 101, 220408(R) (2020)

$E_8$ Spectra of Quasi-one-dimensional Antiferromagnet BaCo$_2$V$_2$O$_8$ under Transverse Field

Authors: Haiyuan Zou, Y. Cui, X. Wang, Z. Zhang, J. Yang, G. Xu, A. Okutani, M. Hagiwara, M. Matsuda, G. Wang, G. Mussardo, K. Hódsági, M. Kormos, Z. Z. He, S. Kimura, Rong Yu, Weiqiang Yu, Jie Ma, Jianda Wu

Abstract: We report $^{51}$V nuclear magnetic resonance (NMR) and inelastic neutron scattering (INS) measurements on a quasi-1D antiferromagnet BaCo$_2$V$_2$O$_8$ under transverse field along the [010] direction. The scaling behavior of the spin-lattice relaxation rate above the Néel temperatures unveils a 1D quantum critical point (QCP) at $H_c^{1D}\approx 4.7$ T, which is masked by the 3D magnetic order.… ▽ More We report $^{51}$V nuclear magnetic resonance (NMR) and inelastic neutron scattering (INS) measurements on a quasi-1D antiferromagnet BaCo$_2$V$_2$O$_8$ under transverse field along the [010] direction. The scaling behavior of the spin-lattice relaxation rate above the Néel temperatures unveils a 1D quantum critical point (QCP) at $H_c^{1D}\approx 4.7$ T, which is masked by the 3D magnetic order. With the aid of accurate analytical analysis and numerical calculations, we show that the zone center INS spectrum at $H_c^{1D}$ is precisely described by the pattern of the 1D quantum Ising model in a magnetic field, a class of universality described in terms of the exceptional $E_8$ Lie algebra. These excitations keep to be non-diffusive over a certain field range when the system is away from the 1D QCP. Our results provide an unambiguous experimental realization of the massive $E_8$ phase in the compound, and open new experimental route for exploring the dynamics of quantum integrable systems as well as physics beyond integrability. △ Less

Submitted 10 August, 2021; v1 submitted 27 May, 2020; originally announced May 2020.

Comments: 6 pages, 4 figures. Supplemental Material is in other format

Journal ref: Phys. Rev. Lett. 127, 077201 (2021)

Anisotropic effect of a magnetic field on the neutron spin resonance in FeSe

Authors: Tong Chen, Youzhe Chen, David W. Tam, Bin Gao, Yiming Qiu, Astrid Schneidewind, Igor Radelytskyi, Karel Prokes, Songxue Chi, Masaaki Matsuda, Collin Broholm, Pengcheng Dai

Abstract: We use inelastic neutron scattering to study the effect of a magnetic field on the neutron spin resonance (Er = 3.6 meV) of superconducting FeSe (Tc = 9 K). While a field aligned along the in-plane direction broadens and suppresses the resonance, a c-axis aligned field does so much more efficiently, consistent with the anisotropic field-induced suppression of the superfluid density from the heat c… ▽ More We use inelastic neutron scattering to study the effect of a magnetic field on the neutron spin resonance (Er = 3.6 meV) of superconducting FeSe (Tc = 9 K). While a field aligned along the in-plane direction broadens and suppresses the resonance, a c-axis aligned field does so much more efficiently, consistent with the anisotropic field-induced suppression of the superfluid density from the heat capacity measurements. These results suggest that the resonance in FeSe is associated with the superconducting electrons arising from orbital selective quasi-particle excitations between the hole and electron Fermi surfaces. △ Less

Submitted 25 March, 2020; originally announced March 2020.

Comments: To be published as a Rapid Communication in Physical Review B

Evolution of the structural transition in Mo$_{1-x}$W$_{x}$Te$_{2}$

Authors: John A. Schneeloch, Yu Tao, Chunruo Duan, Masaaki Matsuda, Adam A. Aczel, Jaime A. Fernandez-Baca, Guangyong Xu, Jörg C. Neuefeind, Junjie Yang, Despina Louca

Abstract: The composition dependence of the structural transition between the monoclinic 1T$^{\prime}$ and orthorhombic T$_{d}$ phases in the Mo$_{1-x}$W$_{x}$Te$_{2}$ Weyl semimetal was investigated by elastic neutron scattering on single crystals up to $x \approx 0.54$. First observed in MoTe$_{2}$, the transition from T$_{d}$ to 1T$^{\prime}$ is accompanied by an intermediate pseudo-orthorhombic phase, T… ▽ More The composition dependence of the structural transition between the monoclinic 1T$^{\prime}$ and orthorhombic T$_{d}$ phases in the Mo$_{1-x}$W$_{x}$Te$_{2}$ Weyl semimetal was investigated by elastic neutron scattering on single crystals up to $x \approx 0.54$. First observed in MoTe$_{2}$, the transition from T$_{d}$ to 1T$^{\prime}$ is accompanied by an intermediate pseudo-orthorhombic phase, T$_{d}^{*}$. Upon doping with W, the T$_{d}^{*}$ phase vanishes by $x \approx 0.34$. Above this concentration, a phase coexistence behavior with both T$_{d}$ and 1T$^{\prime}$ is observed instead. The interlayer in-plane positioning parameter $δ$, which relates to the 1T$^{\prime}$ $β$ angle, decreases with temperature as well as with W substitution, likely due to strong anharmonicity in the interlayer interactions. The temperature width of the phase coexistence remains almost constant up to $x \approx 0.54$, in contrast to the broadening reported under pressure. △ Less

Submitted 11 June, 2020; v1 submitted 18 March, 2020; originally announced March 2020.

Comments: supplement in separate file

Journal ref: Phys. Rev. B 102, 054105 (2020)

Helimagnetic Structure and Heavy-Fermion-Like Behavior in the Vicinity of the Quantum Critical Point in Mn$_3$P

Authors: H. Kotegawa, M. Matsuda, F. Ye, Y. Tani, K. Uda, Y. Kuwata, H. Tou, E. Matsuoka, H. Sugawara, T. Sakurai, H. Ohta, H. Harima, K. Takeda, J. Hayashi, S. Araki, T. C. Kobayashi

Abstract: Antiferromagnet Mn$_3$P with Neel temperature $T_N=30$ K is composed of Mn-tetrahedrons and zigzag chains formed by three inequivalent Mn sites. Due to the nearly frustrated lattice with many short Mn-Mn bonds, competition of the exchange interactions is expected. We here investigate the magnetic structure and physical properties including pressure effect in single crystals of this material, and r… ▽ More Antiferromagnet Mn$_3$P with Neel temperature $T_N=30$ K is composed of Mn-tetrahedrons and zigzag chains formed by three inequivalent Mn sites. Due to the nearly frustrated lattice with many short Mn-Mn bonds, competition of the exchange interactions is expected. We here investigate the magnetic structure and physical properties including pressure effect in single crystals of this material, and reveal a complex yet well-ordered helimagnetic structure. The itinerant character of this materials is strong, and the ordered state with small magnetic moments is easily suppressed under pressure, exhibiting a quantum critical point at $\sim1.6$ GPa. The remarkable mass renormalization, even in the ordered state, and an incoherent-coherent crossover in the low-temperature region, characterize an unusual electronic state in Mn$_3$P, which is most likely effected by the underlying frustration effect. △ Less

Submitted 28 January, 2020; v1 submitted 21 January, 2020; originally announced January 2020.

Comments: 10 pages, 12 figures, including the Supplemental Material, to be published in Physical Review Letters

Journal ref: Phys. Rev. Lett. 124, 087202 (2020)

A-type Antiferromagnetic order in MnBi4Te7 and MnBi6Te10 single crystals

Authors: J. -Q. Yan, Y. H. Liu, D. Parker, Y. Wu, A. A. Aczel, M. Matsuda, M. A. McGuire, B. C. Sales

Abstract: MnBi$_4$Te$_{7}$ and MnBi$_6$Te$_{10}$ are two members with n=2 and 3 in the family of MnBi$_{2n}$Te$_{3n+1}$ where the n=1 member, MnBi$_2$Te$_{4}$, has been intensively investigated as the first intrinsic antiferromagnetic topological insulator. Here we report the A-type antiferromagnetic order in these two compounds by measuring magnetic properties, electrical and thermal transport, specific he… ▽ More MnBi$_4$Te$_{7}$ and MnBi$_6$Te$_{10}$ are two members with n=2 and 3 in the family of MnBi$_{2n}$Te$_{3n+1}$ where the n=1 member, MnBi$_2$Te$_{4}$, has been intensively investigated as the first intrinsic antiferromagnetic topological insulator. Here we report the A-type antiferromagnetic order in these two compounds by measuring magnetic properties, electrical and thermal transport, specific heat, and single crystal neutron diffraction. Both compounds order into an A-type antiferromagnetic structure as does MnBi$_2$Te$_{4}$ with ferromagnetic planes coupled antiferromagnetically along the crystallographic \textit{c} axis. While no evidence for any in-plane ordered moment is found for MnBi$_2$Te$_{4}$ or MnBi$_6$Te$_{10}$, weak reflections at half-L positions along the [0 0 L] direction are observed for MnBi$_4$Te$_{7}$ suggesting an in-plane ordered moment around 0.15$μ_{B}$/Mn. The ordering temperature, T$_N$, is 13\,K for MnBi$_4$Te$_{7}$ and 11\,K for MnBi$_6$Te$_{10}$. The magnetic order is also manifested in the anisotropic magnetic properties. For both compounds, the interlayer coupling is weak and a spin flip transition occurs when a magnetic field of around 1.6\,kOe is applied along the \textit{c}-axis at 2\,K. As observed in MnBi$_2$Te$_4$, when cooling across T$_N$, no anomaly was observed in the temperature dependence of thermopower. On the other hand, critical scattering effects are observed in thermal conductivity although the effect is less pronounced than that in MnBi$_2$Te$_{4}$. △ Less

Submitted 15 April, 2020; v1 submitted 14 October, 2019; originally announced October 2019.

Comments: 15 pages, 14 figures

Journal ref: Phys. Rev. Materials 4, 054202 (2020)

Frustrated magnetic interactions in an S=3/2 bilayer honeycomb lattice compound Bi3Mn4O12(NO3)

Authors: M. Matsuda, S. E. Dissanayake, D. L. Abernathy, Y. Qiu, J. R. D. Copley, N. Kumada, M. Azuma

Abstract: Inelastic neutron scattering study has been performed in an S=3/2 bilayer honeycomb lattice compound Bi3Mn4O12(NO3) at ambient and high magnetic fields. Relatively broad and monotonically dispersive magnetic excitations were observed at ambient field, where no long range magnetic order exists. In the magnetic field-induced long-range ordered state at 10 T, the magnetic dispersions become slightly… ▽ More Inelastic neutron scattering study has been performed in an S=3/2 bilayer honeycomb lattice compound Bi3Mn4O12(NO3) at ambient and high magnetic fields. Relatively broad and monotonically dispersive magnetic excitations were observed at ambient field, where no long range magnetic order exists. In the magnetic field-induced long-range ordered state at 10 T, the magnetic dispersions become slightly more intense, albeit still broad as in the disordered state, and two excitation gaps, probably originating from an easy-plane magnetic anisotropy and intrabilayer interactions, develop. Analyzing the magnetic dispersions using the linear spin-wave theory, we estimated the intraplane and intrabilayer magnetic interactions, which are almost consistent with those determined by ab initio density functional theory calculations [M. Alaei et al., Phys. Rev. B 96, 140404(R) (2017)], except the 3rd and 4th neighbor intrabilayer interactions. Most importantly, as predicted by the theory, there is no significant frustration in the honeycomb plane but frustrating intrabilayer interactions probably give rise to the disordered ground state. △ Less

Submitted 9 October, 2019; originally announced October 2019.

Comments: 8 pages

Highly dispersive magnons with spin-gap like features in the frustrated ferromagnetic S=1/2 chain compound Ca2Y2Cu5O10 detected by inelastic neutron scattering

Authors: M. Matsuda, J. Ma, V. O. Garlea, T. Ito, H. Yamaguchi, K. Oka, S. -L. Drechsler, R. Yadav, L. Hozoi, H. Rosner, R. Schumann, R. O. Kuzian, S. Nishimoto

Abstract: We report inelastic neutron scattering experiments in Ca2Y2Cu5O10 and map out the full one magnon dispersion which extends up to a record value of 53 meV for frustrated ferromagnetic (FM) edge-sharing CuO2 chain (FFESC) cuprates. A homogeneous spin-1/2 chain model with a FM nearest-neighbor (NN), an antiferromagnetic (AFM) next-nearest-neighbor (NNN) inchain, and two diagonal AFM interchain coupli… ▽ More We report inelastic neutron scattering experiments in Ca2Y2Cu5O10 and map out the full one magnon dispersion which extends up to a record value of 53 meV for frustrated ferromagnetic (FM) edge-sharing CuO2 chain (FFESC) cuprates. A homogeneous spin-1/2 chain model with a FM nearest-neighbor (NN), an antiferromagnetic (AFM) next-nearest-neighbor (NNN) inchain, and two diagonal AFM interchain couplings (ICs) analyzed within linear spin-wave theory (LSWT) reproduces well the observed strong dispersion along the chains and a weak one perpendicularly. The ratio R=|J_{a2}/J_{a1}| of the FM NN and the AFM NNN couplings is found as ~0.23, close to the critical point Rc=1/4 which separates ferromagnetically and antiferromagnetically correlated spiral magnetic ground states in single chains, whereas Rc>0.25 for coupled chains is considerably upshifted even for relatively weak IC. Although the measured dispersion can be described by homogeneous LSWT, the scattering intensity appears to be considerably reduced at ~11.5 and ~28 meV. The gap-like feature at 11.5 meV is attributed to magnon-phonon coupling whereas based on DMRG simulations of the dynamical structure factor the gap at 28 meV is considered to stem partly from quantum effects due to the AFM IC. Another contribution is ascribed to the intrinsic superstructure from the distorting incommensurate pattern of CaY cationic chains adjacent to the CuO2 ones. It gives rise to non-equivalent CuO4 units and Cu-O-Cu bond angles Phi and a resulting distribution of all exchange integrals. The J's fitted by homogeneous LSWT are regarded as average values. The record value of the FM NN integral J1=24 meV among FFESC cuprates can be explained by a non-universal Phi (not 90 deg.) and Cu-O bond length dependent anisotropic mean direct FM Cu-O exchange K_{pd}~120 meV. Enhanced K_{pd} values are also needed to compensate a significant AFM J_{dd} > ~6 meV. △ Less

Submitted 8 October, 2019; originally announced October 2019.

Comments: 36 pages

Journal ref: Physical Review B 100, 104415 (2019)

Charge density wave with anomalous temperature dependence in UPt2Si2

Authors: Jooseop Lee, Karel Prokes, Sohee Park, Igor Zaliznyak, Sachith Dissanayake, Masaaki Matsuda, Matthias Frontzek, Stanislav Stoupin, Greta L. Chappell, Ryan E. Baumbach, Changwon Park, John A. Mydosh, Garrett E. Granroth, Jacob P. C. Ruff

Abstract: Using single crystal neutron and x-ray diffraction, we discovered a charge density wave (CDW) below 320 K, which accounts for the long-sought origin of the heat capacity and resistivity anomalies in UPt2Si2. The modulation wavevector, Qmod, is intriguingly similar to the Fermi surface nesting wavevector of URu2Si2. Qmod shows an unusual temperature dependence, shifting from commensurate to incomme… ▽ More Using single crystal neutron and x-ray diffraction, we discovered a charge density wave (CDW) below 320 K, which accounts for the long-sought origin of the heat capacity and resistivity anomalies in UPt2Si2. The modulation wavevector, Qmod, is intriguingly similar to the Fermi surface nesting wavevector of URu2Si2. Qmod shows an unusual temperature dependence, shifting from commensurate to incommensurate position upon cooling and becoming locked at ~ (0.42 0 0) near 180 K. Bulk measurements indicate a cross-over toward a correlated coherent state around the same temperature, suggesting an interplay between the CDW and Kondo-lattice-like coherence before coexisting antiferromagnetic order sets in at TN = 35 K. △ Less

Submitted 29 June, 2020; v1 submitted 8 August, 2019; originally announced August 2019.

Comments: 6 pages, 4 figures

Journal ref: Phys. Rev. B 102, 041112 (2020)

Topological Singularity Induced Chiral Kohn Anomaly in a Weyl Semimetal

Authors: Thanh Nguyen, Fei Han, Nina Andrejevic, Ricardo Pablo-Pedro, Anuj Apte, Yoichiro Tsurimaki, Zhiwei Ding, Kunyan Zhang, Ahmet Alatas, Ercan E. Alp, Songxue Chi, Jaime Fernandez-Baca, Masaaki Matsuda, David Alan Tennant, Yang Zhao, Zhijun Xu, Jeffrey W. Lynn, Shengxi Huang, Mingda Li

Abstract: The electron-phonon interaction (EPI) is instrumental in a wide variety of phenomena in solid-state physics, such as electrical resistivity in metals, carrier mobility, optical transition and polaron effects in semiconductors, lifetime of hot carriers, transition temperature in BCS superconductors, and even spin relaxation in diamond nitrogen-vacancy centers for quantum information processing. How… ▽ More The electron-phonon interaction (EPI) is instrumental in a wide variety of phenomena in solid-state physics, such as electrical resistivity in metals, carrier mobility, optical transition and polaron effects in semiconductors, lifetime of hot carriers, transition temperature in BCS superconductors, and even spin relaxation in diamond nitrogen-vacancy centers for quantum information processing. However, due to the weak EPI strength, most phenomena have focused on electronic properties rather than on phonon properties. One prominent exception is the Kohn anomaly, where phonon softening can emerge when the phonon wavevector nests the Fermi surface of metals. Here we report a new class of Kohn anomaly in a topological Weyl semimetal (WSM), predicted by field-theoretical calculations, and experimentally observed through inelastic x-ray and neutron scattering on WSM tantalum phosphide (TaP). Compared to the conventional Kohn anomaly, the Fermi surface in a WSM exhibits multiple topological singularities of Weyl nodes, leading to a distinct nesting condition with chiral selection, a power-law divergence, and non-negligible dynamical effects. Our work brings the concept of Kohn anomaly into WSMs and sheds light on elucidating the EPI mechanism in emergent topological materials. △ Less

Submitted 15 May, 2020; v1 submitted 2 June, 2019; originally announced June 2019.

Comments: 30 pages, 4 main figures, 11 supplementary figures and 1 theoretical derivation. Feedback most welcome

Journal ref: Phys. Rev. Lett. 124, 236401 (2020)

Magnetization-polarization cross-control near room temperature in hexaferrite single crystals

Authors: Vilmos Kocsis, Taro Nakajima, Masaaki Matsuda, Akiko Kikkawa, Yoshio Kaneko, Junya Takashima, Kazuhisa Kakurai, Taka-hisa Arima, Fumitaka Kagawa, Yusuke Tokunaga, Yoshinori Tokura, Yasujiro Taguchi

Abstract: Mutual control of the electricity and magnetism in terms of magnetic (H) and electric (E) fields, the magnetoelectric (ME) effect, offers versatile low power-consumption alternatives to current data storage, logic gate, and spintronic devices. Despite its importance, E-field control over magnetization (M) with significant magnitude was observed only at low temperatures. Here we have successfully s… ▽ More Mutual control of the electricity and magnetism in terms of magnetic (H) and electric (E) fields, the magnetoelectric (ME) effect, offers versatile low power-consumption alternatives to current data storage, logic gate, and spintronic devices. Despite its importance, E-field control over magnetization (M) with significant magnitude was observed only at low temperatures. Here we have successfully stabilized a simultaneously ferrimagnetic and ferroelectric phase in a Y-type hexaferrite single crystal up to T=450K and demonstrated the reversal of large non-volatile M by E field close to room temperature. Manipulation of the magnetic domains by E field is directly visualized at room temperature by using magnetic force microscopy. The present achievement provides an important step towards the application of bulk ME multiferroics. △ Less

Submitted 10 April, 2019; originally announced April 2019.

Comments: 10 + 9 pages, 5 + 10 figures, Supplementary included

Journal ref: Nature Communicationsvolume 10, Article number: 1247 (2019)

Magnetic competition induced colossal magnetoresistance in n-type HgCr2Se4 under high pressures

Authors: J. P. Sun, Y. Y. Jiao, C. J. Yi, S. E. Dissanayake, M. Matsuda, Y. Uwatoko, Y. G. Shi, Y. Q. Li, Z. Fang, J. -G. Cheng

Abstract: The n-type HgCr2Se4 exhibits a sharp semiconductor-to-metal transition (SMT) in resistivity accompanying the ferromagnetic order at TC = 106 K. Here, we investigate the effects of pressure and magnetic field on the concomitant SMT and ferromagnetic order by measuring resistivity, dc and ac magnetic susceptibility, as well as single-crystal neutron diffraction under various pressures up to 8 GPa an… ▽ More The n-type HgCr2Se4 exhibits a sharp semiconductor-to-metal transition (SMT) in resistivity accompanying the ferromagnetic order at TC = 106 K. Here, we investigate the effects of pressure and magnetic field on the concomitant SMT and ferromagnetic order by measuring resistivity, dc and ac magnetic susceptibility, as well as single-crystal neutron diffraction under various pressures up to 8 GPa and magnetic fields up to 8 T. Our results demonstrate that the ferromagnetic metallic ground state of n-type HgCr2Se4 is destabilized and gradually replaced by an antiferromagnetic, most likely a spiral magnetic, and insulating ground state upon the application of high pressure. On the other hand, the application of external magnetic fields can restore the ferromagnetic metallic state again at high pressures, resulting in a colossal magnetoresistance (CMR) as high as ~ 3 * 10^11 % under 5 T and 2 K at 4 GPa. The present study demonstrates that n-type HgCr2Se4 is located at a peculiar critical point where the balance of competion between ferromagnetic and antiferromagnetic interactions can be easily tipped by the external stimuli, providing a new platform for achieving CMR in a single-valent system. △ Less

Submitted 26 March, 2019; originally announced March 2019.

Comments: 6 pages, 4 figures

Journal ref: Phys. Rev. Lett. 123, 047201 (2019)

Anomalous Magnetic Behavior in Ba2CoO4 with Isolated CoO4 Tetrahedra

Authors: Qiang Zhang, Guixin Cao, Feng Ye, Huibo Cao, Masaaki Matsuda, D. A. Tennant, Songxue Chi, S. E. Nagler, W. A. Shelton, Rongying Jin, E. W. Plummer, Jiandi Zhang

Abstract: The dimensionality of the electronic and magnetic structure of a given material is generally predetermined by its crystal structure. Here, using elastic and inelastic neutron scattering combined with magnetization measurements, we find unusual magnetic behavior in three-dimensional (3D) Ba2CoO4. In spite of isolated CoO4 tetrahedra, the system exhibits a 3D noncollinear antiferromagnetic order in… ▽ More The dimensionality of the electronic and magnetic structure of a given material is generally predetermined by its crystal structure. Here, using elastic and inelastic neutron scattering combined with magnetization measurements, we find unusual magnetic behavior in three-dimensional (3D) Ba2CoO4. In spite of isolated CoO4 tetrahedra, the system exhibits a 3D noncollinear antiferromagnetic order in the ground state with an anomalously large Curie-Weiss temperature of 110 K compared to TN = 26 K. More unexpectedly, spin dynamics displays quasi-2D spin wave dispersion with an unusually large spin gap, and 1D magnetoelastic coupling. Our results indicate that Ba2CoO4 is a unique system for exploring the interplay between isolated polyhedra, low-dimensional magnetism, and novel spin states in oxides. △ Less

Submitted 6 March, 2019; originally announced March 2019.

Comments: to be published in Physical Review B

Coexistence of ferromagnetic and stripe antiferromagnetic spin fluctuations in SrCo$_2$As$_2$

Authors: Yu Li, Zhiping Yin, Zhonghao Liu, Weiyi Wang, Zhuang Xu, Yu Song, Long Tian, Yaobo Huang, Dawei Shen, D. L. Abernathy, J. L. Niedziela, R. A. Ewings, T. G. Perring, Daniel Pajerowski, Masaaki Matsuda, Philippe Bourges, Enderle Mechthild, Yixi Su, Pengcheng Dai

Abstract: We use inelastic neutron scattering to study energy and wave vector dependence of spin fluctuations in SrCo$_2$As$_2$, derived from SrFe$_{2-x}$Co$_x$As$_2$ iron pnictide superconductors. Our data reveals the coexistence of antiferromagnetic (AF) and ferromagnetic (FM) spin fluctuations at wave vectors $\textbf{Q}_{\rm AF}$=(1,0) and $\textbf{Q}_{\rm FM}$=(0,0)/(2,0), respectively. By comparing ne… ▽ More We use inelastic neutron scattering to study energy and wave vector dependence of spin fluctuations in SrCo$_2$As$_2$, derived from SrFe$_{2-x}$Co$_x$As$_2$ iron pnictide superconductors. Our data reveals the coexistence of antiferromagnetic (AF) and ferromagnetic (FM) spin fluctuations at wave vectors $\textbf{Q}_{\rm AF}$=(1,0) and $\textbf{Q}_{\rm FM}$=(0,0)/(2,0), respectively. By comparing neutron scattering results with those of dynamic mean field theory calculation and angle-resolved photoemission spectroscopy experiments, we conclude that both AF and FM spin fluctuations in SrCo$_2$As$_2$ are closely associated with a flat band of the $e_g$ orbitals near the Fermi level, different from the $t_{2g}$ orbitals in superconducting SrFe$_{2-x}$Co$_x$As$_2$. Therefore, Co-substitution in SrFe$_{2-x}$Co$_x$As$_2$ induces a $t_{2g}$ to $e_g$ orbital switching, and is responsible for FM spin fluctuations detrimental to the singlet pairing superconductivity. △ Less

Submitted 27 February, 2019; originally announced February 2019.

Comments: 6 pages, 4 figures, supplemental material available upon request, to be published in PRL

Journal ref: Phys. Rev. Lett. 122, 117204 (2019)