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Tuning THz magnons in a mixed van-der-Waals antiferromagnet
Authors:
F. Le Mardele,
I. Mohelsky,
D. Jana,
A. Pawbake,
J. Dzian,
W. -L. Lee,
K. Raju,
R. Sankar,
C. Faugeras,
M. Potemski,
M. E. Zhitomirsky,
M. Orlita
Abstract:
Alloying stands out as a pivotal technological method employed across various compounds, be they metallic, magnetic, or semiconducting, serving to fine-tune their properties to meet specific requirements. Ternary semiconductors represent a prominent example of such alloys. They offer fine-tuning of electronic bands, the band gap in particular, thus granting the technology of semiconductor heterost…
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Alloying stands out as a pivotal technological method employed across various compounds, be they metallic, magnetic, or semiconducting, serving to fine-tune their properties to meet specific requirements. Ternary semiconductors represent a prominent example of such alloys. They offer fine-tuning of electronic bands, the band gap in particular, thus granting the technology of semiconductor heterostructures devices, key elements in current electronics and optoelectronics. In the realm of magnetically ordered systems, akin to electronic bands in solids, spin waves exhibit characteristic dispersion relations, featuring sizeable magnon gaps in many antiferromagnets. The engineering of the magnon gap constitutes a relevant direction in current research on antiferromagnets, aiming to leverage their distinct properties for THz technologies, spintronics, or magnonics. In this study, we showcase the tunability of the magnon gap across the THz spectral range within an alloy comprising representative semiconducting van-der-Waals antiferromagnets FePS$_3$ and NiPS$_3$. These constituents share identical in-plane crystal structures, magnetic unit cells and the direction of the magnetic anisotropy, but differ in the amplitude and sign of the latter. Altogether these attributes result in the wide tunability of the magnon gap in the Fe$_{1-x}$Ni$_x$PS$_3$ alloy in which the magnetic order is imposed by stronger, perpendicular anisotropy of iron.
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Submitted 4 November, 2024; v1 submitted 22 August, 2024;
originally announced August 2024.
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Lorentz-boost-driven magneto-optics in a Dirac nodal-line semimetal
Authors:
J. Wyzula,
X. Lu,
D. Santos-Cottin,
D. K. Mukherjee,
I. Mohelsky,
F. Le Mardele,
J. Novak,
M. Novak,
R. Sankar,
Y. Krupko,
B. A. Piot,
W. -L. Lee,
A. Akrap,
M. Potemski,
M. O. Goerbig,
M. Orlita
Abstract:
Optical response of crystalline solids is to a large extent driven by excitations that promote electrons among individual bands. This allows one to apply optical and magneto-optical methods to determine experimentally the energy band gap - a fundamental property crucial to our understanding of any solid - with a great precision. Here we show that such conventional methods, applied with great succe…
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Optical response of crystalline solids is to a large extent driven by excitations that promote electrons among individual bands. This allows one to apply optical and magneto-optical methods to determine experimentally the energy band gap - a fundamental property crucial to our understanding of any solid - with a great precision. Here we show that such conventional methods, applied with great success to many materials in the past, do not work in topological Dirac semimetals with a dispersive nodal line. There, the optically deduced band gap depends on how the magnetic field is oriented with respect to the crystal axes. Such highly unusual behaviour is explained in terms of band-gap renormalization driven by Lorentz boosts.
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Submitted 21 July, 2022; v1 submitted 14 October, 2021;
originally announced October 2021.
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Exotic low-energy excitations emergent in the random Kitaev magnet Cu$_2$IrO$_3$
Authors:
Y. S. Choi,
C. H. Lee,
S. Lee,
Sungwon Yoon,
W. -J. Lee,
J. Park,
Anzar Ali,
Yogesh Singh,
Jean-Christophe Orain,
Gareoung Kim,
Jong-Soo Rhyee,
Wei-Tin Chen,
Fangcheng Chou,
Kwang-Yong Choi
Abstract:
We report on magnetization $M(H)$, dc/ac magnetic susceptibility $χ(T)$, specific heat $C_{\mathrm{m}}(T)$ and muon spin relaxation ($μ$SR) measurements of the Kitaev honeycomb iridate Cu$_2$IrO$_2$ with quenched disorder. In spite of the chemical disorders, we find no indication of spin glass down to 260~mK from the $C_{\mathrm{m}}(T)$ and $μ$SR data. Furthermore, a persistent spin dynamics obser…
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We report on magnetization $M(H)$, dc/ac magnetic susceptibility $χ(T)$, specific heat $C_{\mathrm{m}}(T)$ and muon spin relaxation ($μ$SR) measurements of the Kitaev honeycomb iridate Cu$_2$IrO$_2$ with quenched disorder. In spite of the chemical disorders, we find no indication of spin glass down to 260~mK from the $C_{\mathrm{m}}(T)$ and $μ$SR data. Furthermore, a persistent spin dynamics observed by the zero-field muon spin relaxation evidences an absence of static magnetism. The remarkable observation is a scaling relation of $χ[H,T]$ and $M[H,T]$ in $H/T$ with the scaling exponent $α=0.26-0.28$, expected from bond randomness. However, $C_{\mathrm{m}}[H,T]/T$ disobeys the predicted universal scaling law, pointing towards the presence of low-lying excitations in addition to random singlets. Our results signify an intriguing role of quenched disorder in a Kitaev spin system in creating low-energy excitations possibly pertaining to Z$_2$ fluxes.
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Submitted 16 November, 2018;
originally announced November 2018.
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3D Dirac semimetal Cd3As2: A review of material properties
Authors:
I. Crassee,
R. Sankar,
W. -L. Lee,
A. Akrap,
M. Orlita
Abstract:
Cadmium arsenide (Cd3As2) - a time-honored and widely explored material in solid-state physics - has recently attracted considerable attention. This was triggered by a theoretical prediction concerning the presence of 3D symmetry-protected massless Dirac electrons, which could turn Cd3As2 into a 3D analogue of graphene. Subsequent extended experimental studies have provided us with compelling expe…
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Cadmium arsenide (Cd3As2) - a time-honored and widely explored material in solid-state physics - has recently attracted considerable attention. This was triggered by a theoretical prediction concerning the presence of 3D symmetry-protected massless Dirac electrons, which could turn Cd3As2 into a 3D analogue of graphene. Subsequent extended experimental studies have provided us with compelling experimental evidence of conical bands in this system, and revealed a number of interesting properties and phenomena. At the same time, some of the material properties remain the subject of vast discussions despite recent intensive experimental and theoretical efforts, which may hinder the progress in understanding and applications of this appealing material. In this review, we focus on the basic material parameters and properties of Cd3As2, in particular those which are directly related to the conical features in the electronic band structure of this material. The outcome of experimental investigations, performed on Cd3As2 using various spectroscopic and transport techniques within the past sixty years, is compared with theoretical studies. These theoretical works gave us not only simplified effective models, but more recently, also the electronic band structure calculated numerically using ab initio methods.
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Submitted 8 January, 2019; v1 submitted 8 October, 2018;
originally announced October 2018.
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Coincident onset of charge density wave order at a quantum critical point in underdoped YBCO
Authors:
H. Jang,
W. -S. Lee,
S. Song,
H. Nojiri,
S. Matsuzawa,
H. Yasumura,
H. Huang,
Y. -J. Liu,
J. Porras,
M. Minola,
B. Keimer,
J. Hastings,
D. Zhu,
T. P. Devereaux,
Z. -X. Shen,
C. -C. Kao,
J. -S. Lee
Abstract:
The recently demonstrated x-ray scattering approach using a free electron laser with a high field pulsed magnet has opened new opportunities to explore the charge density wave (CDW) order in cuprate high temperature superconductors. Using this approach, we substantially degrade the superconductivity with magnetic fields up to 33 T to investigate the onset of CDW order in YBa$_2$Cu$_3$O$_x$ at low…
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The recently demonstrated x-ray scattering approach using a free electron laser with a high field pulsed magnet has opened new opportunities to explore the charge density wave (CDW) order in cuprate high temperature superconductors. Using this approach, we substantially degrade the superconductivity with magnetic fields up to 33 T to investigate the onset of CDW order in YBa$_2$Cu$_3$O$_x$ at low temperatures near a putative quantum critical point (QCP) at $p_1\sim $ 0.08 holes per Cu. We find no CDW can be detected in a sample with a doping concentration less than $p_1$. Our results indicate that the onset of the CDW ground state lies inside the zero-field superconducting dome, and broken translational symmetry is associated with the putative QCP at $p_1$
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Submitted 20 June, 2018;
originally announced June 2018.
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RIXS studies of magnons and bimagnons in the lightly doped cuprate La2-xSrxCuO4
Authors:
L. Chaix,
E. W. Huang,
S. Gerber,
X. Lu,
C. Jia,
Y. Huang,
D. E. McNally,
Y. Wang,
F. H. Vernay,
A. Keren,
M. Shi,
B. Moritz,
Z. -X. Shen,
T. Schmitt,
T. P. Devereaux,
W. -S. Lee
Abstract:
We investigated the doping dependence of magnetic excitations in the lightly doped cuprate La2-xSrxCuO4 via combined studies of resonant inelastic x-ray scattering (RIXS) at the Cu L3-edge and theoretical calculations. With increasing doping, the magnon dispersion is found to be essentially unchanged, but the spectral width broadens and the spectral weight varies differently at different momenta.…
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We investigated the doping dependence of magnetic excitations in the lightly doped cuprate La2-xSrxCuO4 via combined studies of resonant inelastic x-ray scattering (RIXS) at the Cu L3-edge and theoretical calculations. With increasing doping, the magnon dispersion is found to be essentially unchanged, but the spectral width broadens and the spectral weight varies differently at different momenta. Near the Brillouin zone center, we directly observe bimagnon excitations which possess the same energy scale and doping dependence as previously observed by Raman spectroscopy. They disperse weakly in energy-momentum space, and are consistent with a bimagnon dispersion that is renormalized by the magnon-magnon interaction at the zone center.
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Submitted 2 May, 2018;
originally announced May 2018.
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Putative spin liquid in the triangle-based iridate Ba$_3$IrTi$_2$O$_9$
Authors:
W. -J. Lee,
S. -H. Do,
Sungwon Yoon,
S. Lee,
Y. S. Choi,
D. J. Jang,
M. Brando,
M. Lee,
E. S. Choi,
S. Ji,
Z. H. Jang,
B. J. Suh,
K. -Y. Choi
Abstract:
We report on thermodynamic, magnetization, and muon spin relaxation measurements of the strong spin-orbit coupled iridate Ba$_3$IrTi$_2$O$_9$, which constitutes a new frustration motif made up a mixture of edge- and corner-sharing triangles. In spite of strong antiferromagnetic exchange interaction of the order of 100~K, we find no hint for long-range magnetic order down to 23 mK. The magnetic spe…
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We report on thermodynamic, magnetization, and muon spin relaxation measurements of the strong spin-orbit coupled iridate Ba$_3$IrTi$_2$O$_9$, which constitutes a new frustration motif made up a mixture of edge- and corner-sharing triangles. In spite of strong antiferromagnetic exchange interaction of the order of 100~K, we find no hint for long-range magnetic order down to 23 mK. The magnetic specific heat data unveil the $T$-linear and -squared dependences at low temperatures below 1~K. At the respective temperatures, the zero-field muon spin relaxation features a persistent spin dynamics, indicative of unconventional low-energy excitations. A comparison to the $4d$ isostructural compound Ba$_3$RuTi$_2$O$_9$ suggests that a concerted interplay of compass-like magnetic interactions and frustrated geometry promotes a dynamically fluctuating state in a triangle-based iridate.
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Submitted 11 July, 2017;
originally announced July 2017.
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Ideal charge density wave order in the high-field state of superconducting YBCO
Authors:
H. Jang,
W. -S. Lee,
H. Nojiri,
S. Matsuzawa,
H. Yasumura,
L. Nie,
A. V. Maharaj,
S. Gerber,
Y. Liu,
A. Mehta,
D. A. Bonn,
R. Liang,
W. N. Hardy,
C. A. Burns,
Z. Islam,
S. Song,
J. Hastings,
T. P. Devereaux,
Z. -X. Shen,
S. A. Kivelson,
C. -C. Kao,
D. Zhu,
J. -S. Lee
Abstract:
The existence of charge density wave (CDW) correlations in cuprate superconductors has now been established. However, the nature of the ground state order has remained uncertain because disorder and the presence of superconductivity typically limit the CDW correlation lengths to a dozen unit cells or less. Here we explore the CDW correlations in YBa2Cu3Ox (YBCO) ortho-II and ortho-VIII crystals, w…
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The existence of charge density wave (CDW) correlations in cuprate superconductors has now been established. However, the nature of the ground state order has remained uncertain because disorder and the presence of superconductivity typically limit the CDW correlation lengths to a dozen unit cells or less. Here we explore the CDW correlations in YBa2Cu3Ox (YBCO) ortho-II and ortho-VIII crystals, which belong to the cleanest available cuprate family, at magnetic fields in excess of the resistive upper critical field (Hc2) where the superconductivity is heavily suppressed. We find an incommensurate, unidirectional CDW with a well-defined onset at a critical field strength that is proportional to Hc2. It is related to but distinct from the short-range bidirectional CDW that exists at zero magnetic field. The unidirectional CDW possesses a long inplane correlation length as well as significant correlations between neighboring CuO2 planes, yielding a correlation volume that is at least 2 - 3 orders of magnitude larger than that of the zero-field CDW. This is by far the largest CDW correlation volume observed in any cuprate crystal and so is presumably representative of the high-field ground-state of an "ideal" disorder-free cuprate.
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Submitted 18 July, 2016;
originally announced July 2016.
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Directly characterizing the relative strength and momentum dependence of electron-phonon coupling using resonant inelastic x-ray scattering
Authors:
T. P. Devereaux,
A. M. Shvaika,
K. Wu,
K. Wohlfeld,
C. J. Jia,
Y. Wang,
B. Moritz,
L. Chaix,
W. -S. Lee,
Z. -X. Shen,
G. Ghiringhelli,
L. Braicovich
Abstract:
The coupling between lattice and charge degrees of freedom in condensed matter materials is ubiquitous and can often result in interesting properties and ordered phases, including conventional superconductivity, charge density wave order, and metal-insulator transitions. Angle-resolved photoemission spectroscopy and both neutron and non-resonant x-ray scattering serve as effective probes for deter…
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The coupling between lattice and charge degrees of freedom in condensed matter materials is ubiquitous and can often result in interesting properties and ordered phases, including conventional superconductivity, charge density wave order, and metal-insulator transitions. Angle-resolved photoemission spectroscopy and both neutron and non-resonant x-ray scattering serve as effective probes for determining the behavior of appropriate, individual degrees of freedom -- the electronic structure and lattice excitation, or phonon dispersion, respectively. However, each provides less direct information about the mutual coupling between the degrees of freedom, usual through self-energy effects, which tend to renormalize and broaden spectral features precisely where the coupling is strong, impacting ones ability to quantitively characterize the coupling. Here we demonstrate that resonant inelastic x-ray scattering, or RIXS, can be an effective tool to directly determine the relative strength and momentum dependence of the electron-phonon coupling in condensed matter systems. Using a diagrammatic approach for an 8-band model of copper oxides, we study the contributions from the lowest order diagrams to the full RIXS intensity for a realistic scattering geometry, accounting for matrix element effects in the scattering cross-section as well as the momentum dependence of the electron-phonon coupling vertex. A detailed examination of these maps offers a unique perspective into the characteristics of electron-phonon coupling, which complements both neutron and non-resonant x-ray scattering, as well as Raman and infrared conductivity.
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Submitted 10 May, 2016;
originally announced May 2016.
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Ultrafast Laser-Induced Melting of Long-Range Magnetic Order in Multiferroic TbMnO3
Authors:
Jeremy A. Johnson,
T. Kubacka,
M. C. Hoffmann,
C. Vicario,
S. de Jong,
P. Beaud,
S. Gruebel,
S. -W. Huang,
L. Huber,
Y. W. Windsor,
E. M. Bothschafter,
L. Rettig,
M. Ramakrishnan,
A. Alberca,
L. Patthey,
Y. -D. Chuang,
J. J. Turner,
G. L. Dakovski,
W. -S. Lee,
M. P. Minitti,
W. Schlotter,
R. G. Moore,
C. P. Hauri,
S. M. Koohpayeh,
V. Scagnoli
, et al. (3 additional authors not shown)
Abstract:
We performed ultrafast time-resolved near-infrared pump, resonant soft X-ray diffraction probe measurements to investigate the coupling between the photoexcited electronic system and the spin cycloid magnetic order in multiferroic TbMnO3 at low temperatures. We observe melting of the long range antiferromagnetic order at low excitation fluences with a decay time constant of 22.3 +- 1.1 ps, which i…
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We performed ultrafast time-resolved near-infrared pump, resonant soft X-ray diffraction probe measurements to investigate the coupling between the photoexcited electronic system and the spin cycloid magnetic order in multiferroic TbMnO3 at low temperatures. We observe melting of the long range antiferromagnetic order at low excitation fluences with a decay time constant of 22.3 +- 1.1 ps, which is much slower than the ~1 ps melting times previously observed in other systems. To explain the data we propose a simple model of the melting process where the pump laser pulse directly excites the electronic system, which then leads to an increase in the effective temperature of the spin system via a slower relaxation mechanism. Despite this apparent increase in the effective spin temperature, we do not observe changes in the wavevector q of the antiferromagnetic spin order that would typically correlate with an increase in temperature under equilibrium conditions. We suggest that this behavior results from the extremely low magnon group velocity that hinders a change in the spin-spiral wavevector on these time scales.
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Submitted 23 July, 2015;
originally announced July 2015.
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Three-Dimensional Charge Density Wave Order in YBa2Cu3O6.67 at High Magnetic Fields
Authors:
S. Gerber,
H. Jang,
H. Nojiri,
S. Matsuzawa,
H. Yasumura,
D. A. Bonn,
R. Liang,
W. N. Hardy,
Z. Islam,
A. Mehta,
S. Song,
M. Sikorski,
D. Stefanescu,
Y. Feng,
S. A. Kivelson,
T. P. Devereaux,
Z. -X. Shen,
C. -C. Kao,
W. -S. Lee,
D. Zhu,
J. -S. Lee
Abstract:
Charge density wave (CDW) correlations have recently been shown to universally exist in cuprate superconductors. However, their nature at high fields inferred from nuclear magnetic resonance is distinct from that measured by x-ray scattering at zero and low fields. Here we combine a pulsed magnet with an x-ray free electron laser to characterize the CDW in YBa2Cu3O6.67 via x-ray scattering in fiel…
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Charge density wave (CDW) correlations have recently been shown to universally exist in cuprate superconductors. However, their nature at high fields inferred from nuclear magnetic resonance is distinct from that measured by x-ray scattering at zero and low fields. Here we combine a pulsed magnet with an x-ray free electron laser to characterize the CDW in YBa2Cu3O6.67 via x-ray scattering in fields up to 28 Tesla. While the zero-field CDW order, which develops below T ~ 150 K, is essentially two-dimensional, at lower temperature and beyond 15 Tesla, another three-dimensionally ordered CDW emerges. The field-induced CDW onsets around the zero-field superconducting transition temperature, yet the incommensurate in-plane ordering vector is field-independent. This implies that the two forms of CDW and high-temperature superconductivity are intimately linked.
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Submitted 25 June, 2015;
originally announced June 2015.
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Magnetic excitations and phonons simultaneously studied by resonant inelastic x-ray scattering in optimally doped Bi$_{1.5}$Pb$_{0.55}$Sr$_{1.6}$La$_{0.4}$CuO$_{6+δ}$
Authors:
Y. Y. Peng,
M. Hashimoto,
M. Moretti Sala,
A. Amorese,
N. B. Brookes,
G. Dellea,
W. -S. Lee,
M. Minola,
T. Schmitt,
Y. Yoshida,
K. -J. Zhou,
H. Eisaki,
T. P. Devereaux,
Z. -X. Shen,
L. Braicovich,
G. Ghiringhelli
Abstract:
Magnetic excitations in the optimally doped high-$T_\mathrm{c}$ superconductor Bi$_{1.5}$Pb$_{0.55}$Sr$_{1.6}$La$_{0.4}$CuO$_{6+δ}$ (OP-Bi2201, $T_\mathrm{c}\simeq 34$ K) are investigated by Cu $L_3$ edge resonant inelastic x-ray scattering (RIXS), below and above the pseudogap opening temperature. At both temperatures the broad spectral distribution disperses along the (1,0) direction up to…
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Magnetic excitations in the optimally doped high-$T_\mathrm{c}$ superconductor Bi$_{1.5}$Pb$_{0.55}$Sr$_{1.6}$La$_{0.4}$CuO$_{6+δ}$ (OP-Bi2201, $T_\mathrm{c}\simeq 34$ K) are investigated by Cu $L_3$ edge resonant inelastic x-ray scattering (RIXS), below and above the pseudogap opening temperature. At both temperatures the broad spectral distribution disperses along the (1,0) direction up to $\sim$350~meV at zone boundary, similarly to other hole-doped cuprates. However, above $\sim$0.22 reciprocal lattice units, we observe a concurrent intensity decrease for magnetic excitations and quasi-elastic signals with weak temperature dependence. This anomaly seems to indicate a coupling between magnetic, lattice and charge modes in this compound. We also compare the magnetic excitation spectra near the anti-nodal zone boundary in the single layer OP-Bi2201 and in the bi-layer optimally doped Bi$_{1.5}$Pb$_{0.6}$Sr$_{1.54}$CaCu$_2$O$_{8+δ}$ (OP-Bi2212, $T_\mathrm{c}\simeq96$ K). The strong similarities in the paramagnon dispersion and in their energy at zone boundary indicate that the strength of the super-exchange interaction and the short-range magnetic correlation cannot be directly related to $T_\mathrm{c}$, not even within the same family of cuprates.
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Submitted 20 April, 2015;
originally announced April 2015.
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Direct characterization of photo-induced lattice dynamics in BaFe2As2
Authors:
S. Gerber,
K. W. Kim,
Y. Zhang,
D. Zhu,
N. Plonka,
M. Yi,
G. L. Dakovski,
D. Leuenberger,
P. S. Kirchmann,
R. G. Moore,
M. Chollet,
J. M. Glownia,
Y. Feng,
J. -S. Lee,
A. Mehta,
A. F. Kemper,
T. Wolf,
Y. -D. Chuang,
Z. Hussain,
C. -C. Kao,
B. Moritz,
Z. -X. Shen,
T. P. Devereaux,
W. -S. Lee
Abstract:
Ultrafast light pulses can modify the electronic properties of quantum materials by perturbing the underlying, intertwined degrees of freedom. In particular, iron-based superconductors exhibit a strong coupling among electronic nematic fluctuations, spins, and the lattice, serving as a playground for ultrafast manipulation. Here we use time-resolved x-ray scattering to measure the lattice dynamics…
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Ultrafast light pulses can modify the electronic properties of quantum materials by perturbing the underlying, intertwined degrees of freedom. In particular, iron-based superconductors exhibit a strong coupling among electronic nematic fluctuations, spins, and the lattice, serving as a playground for ultrafast manipulation. Here we use time-resolved x-ray scattering to measure the lattice dynamics of photo-excited BaFe2As2. Upon optical excitation, no signature of an ultrafast change of the crystal symmetry is observed, but the lattice oscillates rapidly in time due to the coherent excitation of an A1g mode that modulates the Fe-As-Fe bond angle. We directly quantify the coherent lattice dynamics and show that even a small photo-induced lattice distortion can induce notable changes in the electronic and magnetic properties. Our analysis implies that transient structural modification can generally be an effective tool for manipulating the electronic properties of multi-orbital systems, where electronic instabilities are sensitive to the orbital character of bands near the Fermi level.
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Submitted 21 December, 2014;
originally announced December 2014.
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Ubiquitous antinodal quasiparticles and deviation from simple d-wave form in underdoped Bi-2212
Authors:
I. M. Vishik,
M. Hashimoto,
W. -S. Lee,
T. P. Devereaux,
Z. -X. Shen
Abstract:
The momentum dependence of the superconducting gap in the cuprates has been debated, with most experiments reporting a deviation from a simple $d_{x^2-y^2}$ form in the underdoped regime and a few experiments claiming that a simple $d_{x^2-y^2}$ form persists down to the lowest dopings. We affirm that the superconducting gap function in sufficiently underdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (Bi-221…
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The momentum dependence of the superconducting gap in the cuprates has been debated, with most experiments reporting a deviation from a simple $d_{x^2-y^2}$ form in the underdoped regime and a few experiments claiming that a simple $d_{x^2-y^2}$ form persists down to the lowest dopings. We affirm that the superconducting gap function in sufficiently underdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ (Bi-2212) deviates from a simple \textit{d}-wave form near the antinode. This is observed in samples where doping is controlled only by oxygen annealing, in contrast to claims that this effect is only seen in cation-substituted samples. Moreover, a quasiparticle peak is present at the antinode down to p$=$0.08, refuting claims that a deviation from a simple \textit{d}-wave form is a data analysis artifact stemming from difficulty in assessing a gap in the absence of a quasiparticle.
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Submitted 1 August, 2017; v1 submitted 20 May, 2014;
originally announced May 2014.
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Direct observation of bulk charge modulations in optimally-doped Bi$_{1.5}$Pb$_{0.6}$Sr$_{1.54}$CaCu$_{2}$O$_{8+δ}$
Authors:
M. Hashimoto,
G. Ghiringhelli,
W. -S. Lee,
G. Dellea,
A. Amorese,
C. Mazzoli,
K. Kummer,
N. B. Brookes,
B. Moritz,
Y. Yoshida,
H. Eisaki,
Z. Hussain,
T. P. Devereaux,
Z. -X. Shen,
L. Braicovich
Abstract:
Bulk charge density modulations, recently observed in high critical-temperature ($T_\mathrm{c}$) cuprate superconductors, coexist with the so-called pseudogap and compete with superconductivity. However, its direct observation has been limited to a narrow doping region in the underdoped regime. Using energy-resolved resonant x-ray scattering we have found evidence for such bulk charge modulations,…
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Bulk charge density modulations, recently observed in high critical-temperature ($T_\mathrm{c}$) cuprate superconductors, coexist with the so-called pseudogap and compete with superconductivity. However, its direct observation has been limited to a narrow doping region in the underdoped regime. Using energy-resolved resonant x-ray scattering we have found evidence for such bulk charge modulations, or soft collective charge modes (soft CCMs), in optimally doped Bi$_{1.5}$Pb$_{0.6}$Sr$_{1.54}$CaCu$_{2}$O$_{8+δ}$ (Pb-Bi2212) around the summit of the superconducting dome with momentum transfer $q_{\parallel}\sim0.28$ reciprocal lattice units (r.l.u.) along the Cu-O bond direction. The signal is stronger at $T\simeq T_\mathrm{c}$ than at lower temperatures, thereby confirming a competition between soft CCMs and superconductivity. These results demonstrate that soft CCMs are not constrained to the underdoped regime, suggesting that soft CCMs appear across a large part of the phase diagram of cuprates and are intimately entangled with high-$T_\mathrm{c}$ superconductivity.
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Submitted 30 June, 2014; v1 submitted 1 March, 2014;
originally announced March 2014.
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Time-Dependent Charge-Order and Spin-Order Recovery in Striped Systems
Authors:
Y. F. Kung,
W. -S. Lee,
C. -C. Chen,
A. F. Kemper,
A. P. Sorini,
B. Moritz,
T. P. Devereaux
Abstract:
Using time-dependent Ginzburg-Landau theory, we study the role of amplitude and phase fluctuations in the recovery of charge and spin stripe phases in response to a pump pulse that melts the orders. For parameters relevant to the case where charge order precedes spin order thermodynamically, amplitude recovery governs the initial time scales, while phase recovery controls behavior at longer times.…
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Using time-dependent Ginzburg-Landau theory, we study the role of amplitude and phase fluctuations in the recovery of charge and spin stripe phases in response to a pump pulse that melts the orders. For parameters relevant to the case where charge order precedes spin order thermodynamically, amplitude recovery governs the initial time scales, while phase recovery controls behavior at longer times. In addition to these intrinsic effects, there is a longer spin re-orientation time scale related to the scattering geometry that dominates the recovery of the spin phase. Coupling between the charge and spin orders locks the amplitude and similarly the phase recovery, reducing the number of distinct time scales. Our results well reproduce the major experimental features of pump-probe x-ray diffraction measurements on the striped nickelate La$_{1.75}$Sr$_{0.25}$NiO$_4$. They highlight the main idea of this work, which is the use of time-dependent Ginzburg-Landau theory to study systems with multiple coexisting order parameters.
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Submitted 9 September, 2013; v1 submitted 14 June, 2013;
originally announced June 2013.
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Femtosecond dynamics of the collinear-to-spiral antiferromagnetic phase transition in CuO
Authors:
S. L. Johnson,
R. A. de Souza,
U. Staub,
P. Beaud,
E. Möhr-Vorobeva,
G. Ingold,
A. Caviezel,
V. Scagnoli,
W. F. Schlotter,
J. J. Turner,
O. Krupin,
W. -S. Lee,
Y. -D. Chuang,
L. Patthey,
R. G. Moore,
D. Lu,
M. Yi,
P. S. Kirchmann,
M. Trigo,
P. Denes,
D. Doering,
Z. Hussain,
Z. -X. Shen,
D. Prabhakaran,
A. T. Boothroyd
Abstract:
We report on the ultrafast dynamics of magnetic order in a single crystal of CuO at a temperature of 207 K in response to strong optical excitation using femtosecond resonant x-ray diffraction. In the experiment, a femtosecond laser pulse induces a sudden, nonequilibrium increase in magnetic disorder. After a short delay ranging from 400 fs to 2 ps, we observe changes in the relative intensity of…
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We report on the ultrafast dynamics of magnetic order in a single crystal of CuO at a temperature of 207 K in response to strong optical excitation using femtosecond resonant x-ray diffraction. In the experiment, a femtosecond laser pulse induces a sudden, nonequilibrium increase in magnetic disorder. After a short delay ranging from 400 fs to 2 ps, we observe changes in the relative intensity of the magnetic ordering diffraction peaks that indicate a shift from a collinear commensurate phase to a spiral incommensurate phase. These results indicate that the ultimate speed for this antiferromagnetic re-orientation transition in CuO is limited by the long-wavelength magnetic excitation connecting the two phases.
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Submitted 2 December, 2011; v1 submitted 30 June, 2011;
originally announced June 2011.
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Capacitive interaction model for Aharonov-Bohm effects of a quantum Hall antidot
Authors:
W. -R. Lee,
H. -S. Sim
Abstract:
We derive a general capacitive interaction model for an antidot-based interferometer in the integer quantum Hall regime, and study Aharonov-Bohm resonances in a single antidot with multiple bound modes, as a function of the external magnetic field or the gate voltage applied to the antidot. The pattern of Aharonov-Bohm resonances is significantly different from the case of noninteracting electrons…
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We derive a general capacitive interaction model for an antidot-based interferometer in the integer quantum Hall regime, and study Aharonov-Bohm resonances in a single antidot with multiple bound modes, as a function of the external magnetic field or the gate voltage applied to the antidot. The pattern of Aharonov-Bohm resonances is significantly different from the case of noninteracting electrons. The origin of the difference includes charging effects of excess charges, charge relaxation between the bound modes, the capacitive interaction between the bound modes and the extended edge channels nearby the antidot, and the competition between the single-particle level spacing and the charging energy of the antidot. We analyze the patterns for the case that the number of the bound modes is 2, 3, or 4. The results agree with recent experimental data.
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Submitted 14 January, 2011; v1 submitted 6 September, 2010;
originally announced September 2010.
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Spectator Behavior in a Quantum Hall Antidot with Multiple Bound Modes
Authors:
W. -R. Lee,
H. -S. Sim
Abstract:
We theoretically study Aharonov-Bohm resonances in an antidot system with multiple bound modes in the integer quantum Hall regime, taking capacitive interactions between the modes into account. We find the spectator behavior that the resonances of some modes disappear and instead are replaced by those of other modes, due to internal charge relaxation between the modes. This behavior is a possible…
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We theoretically study Aharonov-Bohm resonances in an antidot system with multiple bound modes in the integer quantum Hall regime, taking capacitive interactions between the modes into account. We find the spectator behavior that the resonances of some modes disappear and instead are replaced by those of other modes, due to internal charge relaxation between the modes. This behavior is a possible origin of the features of previous experimental data which remain unexplained, spectator behavior in an antidot molecule and resonances in a single antidot with three modes.
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Submitted 4 May, 2010;
originally announced May 2010.
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Evidence for weak electronic correlations in Fe-pnictides
Authors:
W. L. Yang,
P. O. Velasco,
J. D. Denlinger,
A. P. Sorini,
C-C. Chen,
B. Moritz,
W. -S. Lee,
F. Vernay,
B. Delley,
J. -H. Chu,
J. G. Analytis,
I. R. Fisher,
Z. A. Ren,
J. Yang,
W. Lu,
Z. X. Zhao,
J. van den Brink,
Z. Hussain,
Z. -X. Shen,
T. P. Devereaux
Abstract:
Using x-ray absorption and resonant inelastic x-ray scattering, charge dynamics at and near the Fe $L$ edges is investigated in Fe pnictide materials, and contrasted to that measured in other Fe compounds. It is shown that the XAS and RIXS spectra for 122 and 1111 Fe pnictides are each qualitatively similar to Fe metal. Cluster diagonalization, multiplet, and density-functional calculations show…
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Using x-ray absorption and resonant inelastic x-ray scattering, charge dynamics at and near the Fe $L$ edges is investigated in Fe pnictide materials, and contrasted to that measured in other Fe compounds. It is shown that the XAS and RIXS spectra for 122 and 1111 Fe pnictides are each qualitatively similar to Fe metal. Cluster diagonalization, multiplet, and density-functional calculations show that Coulomb correlations are much smaller than in the cuprates, highlighting the role of Fe metallicity and strong covalency in these materials. Best agreement with experiment is obtained using Hubbard parameters $U\lesssim 2$eV and $J\approx 0.8$eV.
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Submitted 15 May, 2009;
originally announced May 2009.
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Revival of electron coherence in a finite-length quantum wire
Authors:
Jaeuk U. Kim,
W. -R. Lee,
Hyun-Woo Lee,
H. -S. Sim
Abstract:
We study the spatial decay of electron coherence due to electron-electron interaction in a finite-length disorder-free quantum wire. Based on the Luttinger liquid theory, we demonstrate that the coherence length characterizing the exponential decay of the coherence can vary from region to region, and that the coherence can even revive after the decay. This counterintuitive behavior, which is in…
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We study the spatial decay of electron coherence due to electron-electron interaction in a finite-length disorder-free quantum wire. Based on the Luttinger liquid theory, we demonstrate that the coherence length characterizing the exponential decay of the coherence can vary from region to region, and that the coherence can even revive after the decay. This counterintuitive behavior, which is in clear contrast to the conventional exponential decay with single coherence length, is due to the fractionalization of an electron and the finite-size-induced recombination of the fractions.
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Submitted 17 January, 2009;
originally announced January 2009.
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Fano resonance in a two-level quantum dot side-coupled to leads
Authors:
W. -R. Lee,
Jaeuk U. Kim,
H. -S. Sim
Abstract:
We theoretically study Fano resonance in a two-level quantum dot side-coupled to two leads, which are connected by a direct channel. The resonance lineshape is found to be deformed, from the conventional Fano form, by interlevel Coulomb interaction and interlevel interference. We derive the connection between the lineshape deformation and the interaction-induced nonmonotonicity of level occupati…
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We theoretically study Fano resonance in a two-level quantum dot side-coupled to two leads, which are connected by a direct channel. The resonance lineshape is found to be deformed, from the conventional Fano form, by interlevel Coulomb interaction and interlevel interference. We derive the connection between the lineshape deformation and the interaction-induced nonmonotonicity of level occupation, which may be useful for experimental study. The dependence of the lineshape on the transmission of the direct channel and on the dot-lead coupling matrix elements is discussed.
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Submitted 16 October, 2007;
originally announced October 2007.
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Measuring Lateral Magnetic Structure in Thin Films Using Polarized Neutron Reflectometry
Authors:
W. -T. Lee,
S. G. E. te Velthuis,
G. P. Felcher,
F. Klose,
T. Gredig,
D. Dahlberg,
B. V. Toperverg
Abstract:
Polarized neutron reflectometry (PNR) has long been applied to measure the magnetic depth profile of thin films. In recent years, interest has increased in observing lateral magnetic structures in a film. While magnetic arrays patterned by lithography and submicron-sized magnetic domains in thin films often give rise to off-specular reflections, micron-sized ferromagnetic domains on a thin film…
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Polarized neutron reflectometry (PNR) has long been applied to measure the magnetic depth profile of thin films. In recent years, interest has increased in observing lateral magnetic structures in a film. While magnetic arrays patterned by lithography and submicron-sized magnetic domains in thin films often give rise to off-specular reflections, micron-sized ferromagnetic domains on a thin film produce few off-specular reflections and the domain distribution information is contained within the specular reflection. In this paper, we will first present some preliminary results of off-specular reflectivity from arrays of micron-sized permalloy rectangular bars. We will then use specular reflections to study the domain dispersion of an exchange-biased Co/CoO bilayer at different locations of the hysteresis loop.
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Submitted 6 October, 2002;
originally announced October 2002.
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Ferromagnetic Domain Distribution in Thin Films During Magnetization Reversal
Authors:
W. -T. Lee,
S. G. E. te Velthuis,
G. P. Felcher,
F. Klose,
T. Gredig,
E. D. Dahlberg
Abstract:
We have shown that polarized neutron reflectometry can determine in a model-free way not only the mean magnetization of a ferromagnetic thin film at any point of a hysteresis cycle, but also the mean square dispersion of the magnetization vectors of its lateral domains. This technique is applied to elucidate the mechanism of the magnetization reversal of an exchange-biased Co/CoO bilayer. The re…
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We have shown that polarized neutron reflectometry can determine in a model-free way not only the mean magnetization of a ferromagnetic thin film at any point of a hysteresis cycle, but also the mean square dispersion of the magnetization vectors of its lateral domains. This technique is applied to elucidate the mechanism of the magnetization reversal of an exchange-biased Co/CoO bilayer. The reversal process above the blocking temperature is governed by uniaxial domain switching, while below the blocking temperature the reversal of magnetization for the trained sample takes place with substantial domain rotation.
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Submitted 21 May, 2001; v1 submitted 2 May, 2001;
originally announced May 2001.