Showing 1–17 of 17 results for author: Arh, T

Lifting the degeneracy of quantum spin liquid phase by uniaxial pressure

Authors: Shams Sohel Islam, Zurab Guguchia, Orion Gerguri, Petr Král, Maxime Lamotte, Toni Shiroka, Jonas A. Krieger, Thomas J. Hicken, Tina Arh, Gediminas Simutis, Abanoub Hanna, Nazmul Islam, Bella Lake, Hubertus Luetkens, Hans Henning Klauss, Rajib Sarkar

Abstract: We report muon spin relaxation/rotation ($μ$SR) measurements of the candidate three-dimensional (3D) quantum spin liquid (QSL) PbCuTe$_2$O$_6$, hosting $S=1/2$ moments, under controlled in situ [110] uniaxial compression up to $σ_{[110]}=37.7$~MPa. A small directional lattice perturbation significantly modifies the local magnetic response, while above $σ_{\rm cr}\sim10.8$\,MPa the relaxation rates… ▽ More We report muon spin relaxation/rotation ($μ$SR) measurements of the candidate three-dimensional (3D) quantum spin liquid (QSL) PbCuTe$_2$O$_6$, hosting $S=1/2$ moments, under controlled in situ [110] uniaxial compression up to $σ_{[110]}=37.7$~MPa. A small directional lattice perturbation significantly modifies the local magnetic response, while above $σ_{\rm cr}\sim10.8$\,MPa the relaxation rates are strongly enhanced and the internal-field distribution is substantially broadened. These changes occur along with the local crystalline symmetry breaking. While, no evidence for conventional static long-range magnetic order is observed, the compression drives the system towards a structurally modified and strongly correlated state in which enhanced quasi-static correlations coexist with persistent slow spin dynamics. This work demonstrates a clean and symmetry-selective route to control frustrated exchange landscape and access hidden magnetic instabilities in a 3D QSL candidate opening up the possibilities to tune other correlated systems where intrinsic coupling between magnetic and lattice degrees of freedom are relevant. △ Less

Submitted 5 August, 2026; originally announced August 2026.

Comments: 7 pages, 4 figures. The supplementary information has not been uploaded in the current version

Quantum spin liquid on a 3D bipartite lattice of spin trimers stabilized by enhanced effective anisotropy

Authors: M. Gomilšek, L. Mangin-Thro, T. Arh, S. Petit, B. Grenier, V. Simonet, M. Pregelj, A. Zorko, B. Koteswararao, B. -G. Jeon, B. Sana, Y. Furukawa, Y. Inagaki, T. Asano, C. Repellin, B. Fåk, J. Ollivier, F. Fauth, C. V. Colin, E. Pachoud, V. Pomjakushin, J. S. Lord, H. Luetkens, K. -H. Kim, P. Khuntia

Abstract: Quantum spin liquids (QSLs) represent highly entangled states of matter in which frustration-induced quantum fluctuations suppress any symmetry-breaking phase transition down to absolute zero, giving rise to fractionalized excitations and emergent gauge fields. Theoretically, bond anisotropy can stabilize QSLs even on bipartite lattices, as exemplified by the Kitaev honeycomb model; however, no ma… ▽ More Quantum spin liquids (QSLs) represent highly entangled states of matter in which frustration-induced quantum fluctuations suppress any symmetry-breaking phase transition down to absolute zero, giving rise to fractionalized excitations and emergent gauge fields. Theoretically, bond anisotropy can stabilize QSLs even on bipartite lattices, as exemplified by the Kitaev honeycomb model; however, no material has so far been established to realize such a state as its true ground state. Here we identify the three-dimensional spin-trimer magnet KBa$_3$Ca$_4$Cu$_3$V$_7$O$_{28}$ as a promising candidate for a bipartite quantum spin liquid persisting to the lowest temperatures. Strongly coupled Cu$^{2+}$ trimers form effective pseudospin-1/2 degrees of freedom upon cooling, which in turn constitute a three-dimensional bipartite network. Bulk thermodynamic measurements, neutron scattering, $μ$SR, and NMR detect no spin freezing or symmetry-breaking phase transition down to 20 mK, but instead reveal a gapless dynamical ground state with algebraic spin autocorrelations. Complementary Monte Carlo and exact-diagonalization calculations show that this state is stabilized by a strong enhancement of effective anisotropy: a weak microscopic Cu-Cu exchange anisotropy of approximately 15 percent is generically amplified at the trimer level, producing effective pseudospin-pseudospin interaction anisotropies of 60 to 100 percent. Our results establish trimer-based networks as a promising platform for realizing anisotropy-stabilized quantum entangled states, even in three-dimensional bipartite systems with only weak microscopic anisotropy. △ Less

Submitted 7 May, 2026; originally announced May 2026.

Melting upon cooling in a quantum magnet

Authors: K. Jaksetič, T. Arh, M. Pregelj, M. Gomilšek, M. Dragomir, P. Prelovšek, M. Ulaga, L. Šibav, M. Malovrh, K. Železnikar, Z. Jagličić, P. Manuel, F. Orlandi, D. Khalyavin, M. D. Le, N. Bujault, E. Lhotel, J. van Tol, U. Jena, B. Sana, P. Khuntia, A. Zorko

Abstract: Heating enhances thermal fluctuations and typically leads to melting of solids, but in exceptional cases, heating can also cause liquids to solidify. The paradigm of this counterintuitive phenomenon is solidification of liquid $^3$He upon increasing temperature, known as the Pomeranchuk effect. Here we show that such inverse melting also appears in quantum magnetism. We find that, on cooling, the… ▽ More Heating enhances thermal fluctuations and typically leads to melting of solids, but in exceptional cases, heating can also cause liquids to solidify. The paradigm of this counterintuitive phenomenon is solidification of liquid $^3$He upon increasing temperature, known as the Pomeranchuk effect. Here we show that such inverse melting also appears in quantum magnetism. We find that, on cooling, the Ising-like triangular-lattice antiferromagnet erbium heptatantalate first develops a three-sublattice long-range magnetic order -- analogous to a solid -- which then, unexpectedly, melts at even lower temperatures into a short-range correlated spin-stripe state -- analogous to a liquid. We propose that such an unprecedented ``spin Pomeranchuk effect" can generically arise from strong competition between spin-spin interactions in frustrated magnets, and provides a novel avenue to transformations between exotic magnetic phases. △ Less

Submitted 6 May, 2026; originally announced May 2026.

Magnetic and phononic dynamics in the two-ladder quantum magnet (C5H9NH3)2CuBr4

Authors: J. Philippe, F. Elson, T. Arh, S. Sanz, M. Metzelaars, D. W. Tam, O. K. Forslund, O. Shliakhtun, C. Jiang, J. Lass, M. D. Le, J. Ollivier, P. Bouillot, T. Giamarchi, M. Bartkowiak, D. G. Mazzone, P. Kögerler, M. Månsson, A. M. Läuchli, Y. Sassa, M. Janoschek, B. Normand, G. Simutis

Abstract: In quantum magnetic materials it is common to observe both static and dynamic lattice effects on the magnetic excitation spectrum. Less common is to find that the magnetic correlations have a significant impact on the phonon spectrum. Can such an interplay occur in a structurally soft system with comparable elastic and magnetic energy scales? Here we study the metal-organic material (C5H9NH3)2CuBr… ▽ More In quantum magnetic materials it is common to observe both static and dynamic lattice effects on the magnetic excitation spectrum. Less common is to find that the magnetic correlations have a significant impact on the phonon spectrum. Can such an interplay occur in a structurally soft system with comparable elastic and magnetic energy scales? Here we study the metal-organic material (C5H9NH3)2CuBr4 (Cu-CPA), in which an explanation of the low-lying excitations depends crucially on a full understanding of both the spin and lattice subsystems. We report high-resolution neutron spectroscopy enabled by large, deuterated single-crystals that reveal how both sectors are affected by the recently discovered structural phase transition. By measuring over several Brillouin zones, we disentangle the vibrational contribution to the spectrum in order to obtain an accurate estimate of the quasi-one-dimensional magnetic signal. The low-energy magnetic excitations are dominated by two gaps, $Δ$ b = 0.41 meV and $Δ$ a = 0.55 meV, which contribute with equal intensity ratios, confirming that Cu-CPA realizes a two-ladder spin Hamiltonian, and we deduce the magnetic interaction parameters of both ladders. The phonon spectrum contains a highly localized mode at an anomalously low-energy around 2 meV. This characteristic frequency drops by approximately 5 percent as magnetic correlations become established with decreasing temperature, and we connect this behavior with the location and structure of the cyclopentylammonium rings. △ Less

Submitted 28 October, 2025; originally announced October 2025.

Journal ref: Phys. Rev. B 113, 134438 (2026)

Comment on "Neutron diffraction evidence of the 3-dimensional structure of Ba2MnTeO6 and misidentification of the triangular layers within the face-centred cubic lattice"

Authors: J. Khatua, T. Arh, Shashi B. Mishra, H. Luetkens, A. Zorko, B. Sana, M. S. Ramachandra Rao, B. R. K. Nanda, P. Khuntia

Abstract: Frustrated magnetism continues to attract significant attention due to its potential to host novel quantum many-body phenomena and associated exotic excitations that transcend existing paradigms. Herein, we present our reply to the comment on our recent thermodynamic and muon spin relaxation studies on a frustrated double perovskite, Ba2MnTeO6 (henceforth BMTO). Previous studies by four independen… ▽ More Frustrated magnetism continues to attract significant attention due to its potential to host novel quantum many-body phenomena and associated exotic excitations that transcend existing paradigms. Herein, we present our reply to the comment on our recent thermodynamic and muon spin relaxation studies on a frustrated double perovskite, Ba2MnTeO6 (henceforth BMTO). Previous studies by four independent groups, including our group, suggested a trigonal space group based on single-crystal and polycrystalline samples of BMTO, while the recent comment reports a cubic space group based on polycrystalline samples. We believe that the structure is fairly intricate because of the slight variations between the two space groups, refining the crystal structure of BMTO remains an unresolved problem that needs additional high-resolution XRD and neutron diffraction studies on high-quality single crystals. It is thought, however, that structural assignments will not greatly influence any of the primary findings related to the magnetism and spin dynamics of BMTO. These consist of a magnetic phase transition at around 21 K, the observation of antiferromagnetic magnon excitations exhibiting a gap of 1.4 K beneath the phase transition, the presence of short-range spin correlations well above the antiferromagnetic phase transition, and the persistence of spin dynamics even within the magnetically ordered phase. It is important to note that the magnetization, specific heat, and muon spin relaxation findings that constitute the core of our earlier study are independent; the interpretation of these findings did not rely on any specific space group. Concerning the final allocation of the symmetry of BMTO, a definitive differentiation in certain physical characteristics resulting from the symmetry is still necessary. △ Less

Submitted 2 June, 2025; originally announced June 2025.

Comments: Comment on arXiv:2202.03850

Journal ref: Scientific Reports (Nature) 16, 7957 (2026)

Optimized flux single-crystal growth of the quantum spin liquid candidate NdTa$_7$O$_{19}$ and other rare-earth heptatantalates, ErTa$_7$O$_{19}$ and GdTa$_7$O$_{19}$

Authors: Lia Šibav, Matic Lozinšek, Zvonko Jagličić, Tina Arh, Panchanana Khuntia, Andrej Zorko, Mirela Dragomir

Abstract: Single crystals are essential for characterizing a wide range of magnetic states, including exotic ones such as quantum spin liquids. This study reports a flux method for growing single crystals of NdTa$_7$O$_{19}$, the first quantum spin liquid candidate on a triangular spin lattice with dominant Ising like spin correlations. Purple NdTa$_7$O$_{19}$ single crystals with hexagonal morphology were… ▽ More Single crystals are essential for characterizing a wide range of magnetic states, including exotic ones such as quantum spin liquids. This study reports a flux method for growing single crystals of NdTa$_7$O$_{19}$, the first quantum spin liquid candidate on a triangular spin lattice with dominant Ising like spin correlations. Purple NdTa$_7$O$_{19}$ single crystals with hexagonal morphology were successfully grown using a K$_2$Mo$_3$O$_{10}$-B$_2$O$_3$ flux. With lateral sizes up to 3.5 mm and a thickness up to 2 mm, these are the largest dimensions reported to date. The chemical composition was confirmed by powder and single-crystal X-ray diffraction along with scanning electron microscopy with energy dispersive X-ray spectroscopy. Aiming for an accurate determination of the magnetic anisotropy and its effect on the magnetic properties, NdTa$_7$O$_{19}$ crystals were additionally analyzed by magnetic susceptibility, revealing a substantial anisotropy without long-range magnetic ordering down to 2 K. Single crystals of two novel rare-earth heptatantalates, ErTa$_7$O$_{19}$ and GdTa$_7$O$_{19}$, were also grown and their magnetic properties investigated. The magnetic anisotropy of ErTa$_7$O$_{19}$ closely resembles that of isostructural NdTa$_7$O$_{19}$, indicating a possibility of a similar exotic magnetic ground state. In contrast, GdTa$_7$O$_{19}$ shows paramagnetic behavior, consistent with previous results obtained for polycrystalline samples. △ Less

Submitted 12 May, 2025; originally announced May 2025.

Comments: 24 pages, 11 figures, supplementary material

Anharmonic quantum muon effects of light particles in a spin liquid material

Authors: Fabian Hotz, Matjaž Gomilšek, Tina Arh, Thomas Hicken, Polona Umek, Andrej Zorko, Hubertus Luetkens

Abstract: The quantum behavior of light nuclei and other particles in materials challenges classical intuition and introduces novel phenomena. Here we demonstrate that muon spin spectroscopy ( $μ$SR) is a powerful tool for exploring the quantum effects of light particles, such as the muon, in condensed matter. The muon's quantum nature is profoundly influenced by the surrounding, offering a unique probe for… ▽ More The quantum behavior of light nuclei and other particles in materials challenges classical intuition and introduces novel phenomena. Here we demonstrate that muon spin spectroscopy ( $μ$SR) is a powerful tool for exploring the quantum effects of light particles, such as the muon, in condensed matter. The muon's quantum nature is profoundly influenced by the surrounding, offering a unique probe for understanding the role of light atoms and their role in shaping local electronic environments. In Zn-barlowite, a candidate quantum spin liquid, we show that standard density functional theory (DFT) methods, which treat the muon as a classical point-like particle, fail to capture its strong quantum anharmonic effects. Only by modeling the muon as a spatially extended quantum particle, thus accounting for the anharmonicity, can the experimental $μ$SR data be understood. This approach not only improves the interpretation of $μ$SR results but also opens the door to studying the quantum effects of other light particles, like hydrogen and lithium nuclei, which can greatly influence material properties. △ Less

Submitted 14 July, 2025; v1 submitted 31 July, 2024; originally announced August 2024.

Magnetic properties and field-induced phenomena in the Jeff = 1/2 distorted kagome antiferromagnet

Authors: A. Yadav, A. Elghandour, T. Arh, D. T. Adroja, M. D. Le, G. B. G. Stenning, M. Aouane, S. Luther, F. Hotz, T. J. Hicken, H. Luetkens, A. Zorko, R. Klingeler, P. Khuntia

Abstract: The intertwining between competing degrees of freedom, anisotropy, and frustration-induced quantum fluctuations offers an ideal ground to realize exotic quantum phenomena in the rare-earth-based kagome lattice. The magnetic susceptibility reveals the presence of two energy scales in agreement with the INS results. The higher energy state is dominated by CEF excitations, where the lowest Kramers gr… ▽ More The intertwining between competing degrees of freedom, anisotropy, and frustration-induced quantum fluctuations offers an ideal ground to realize exotic quantum phenomena in the rare-earth-based kagome lattice. The magnetic susceptibility reveals the presence of two energy scales in agreement with the INS results. The higher energy state is dominated by CEF excitations, where the lowest Kramers ground-state doublet is well separated from the excited state suggesting that the compound realizes a low-energy state at low temperatures. The second energy scale is witnessed via thermodynamic results that reveal an anomaly at 0.3 K typical of a phase transition, which is attributed to the presence of complex magnetic ordering phenomena. The broad maximum in the specific heat well above 0.3 K indicates the presence of short-range spin correlations that is corroborated by muon spin relaxation rate results. The isothermal magnetization reveals a field-induced 1/3 magnetization plateau at low temperatures. muSR relaxation rate experiments, on the other hand, neither show the signature of a phase transition nor spin-freezing down to 34 mK. The ZF muSR relaxation is governed by the Orbach process and reveals the presence of a fluctuating state owing to the depopulation of crystal field levels reflected as a constant value of relaxation rate in the temperature range 0.4-10 K. NMR results indicate the presence of fluctuating Nd3+ moments down to 1.8 K consistent with muSR experiments. Our comprehensive results reveal that a field-induced quantum critical phenomenon is at play in this frustrated kagome magnet and enable us to construct a phase diagram exemplifying the proximity effect of competing magnetic states. This sets the stage to investigate the broad RE3BWO9 family of rare-earth kagome magnets promising to host exotic quantum states driven by spin-orbit coupling and geometrical frustration. △ Less

Submitted 18 December, 2024; v1 submitted 12 July, 2024; originally announced July 2024.

Journal ref: Phys. Rev. B 111, 094408 (2025)

The pairing symmetry in quasi-one-dimensional superconductor Rb2Mo3As3

Authors: Žiga Gosar, Tina Arh, Kevin Jaksetič, Andrej Zorko, Wenhao Liu, Hanlin Wu, Chennan Wang, Hubertus Luetkens, Bing Lv, Denis Arčon

Abstract: Quasi-one-dimensional electron systems display intrinsic instability towards long-range ordered phases at sufficiently low temperatures. The superconducting orders are of particular interest as they can possess either singlet or triplet pairing symmetry and frequently compete with magnetism. Here we report on muon spin rotation and relaxation ($\mathrmμ$SR) study of Rb$_2$Mo$_3$As$_3$ characterise… ▽ More Quasi-one-dimensional electron systems display intrinsic instability towards long-range ordered phases at sufficiently low temperatures. The superconducting orders are of particular interest as they can possess either singlet or triplet pairing symmetry and frequently compete with magnetism. Here we report on muon spin rotation and relaxation ($\mathrmμ$SR) study of Rb$_2$Mo$_3$As$_3$ characterised by one of the highest critical temperatures $T_{\rm c}=10.4\ \mathrm{K}$ among quasi-one-dimensional superconductors. The transverse-field $\mathrmμ$SR signal shows enhanced damping below $T_{\rm c}$ due to the formation of vortex lattice. Comparison of vortex lattice broadening against single gap $s-$, $p-$ and $d-$wave models shows the best agreement for the $s-$wave scenario but with the anomalously small superconducting gap, $Δ_0$, to $T_{\rm c}$ ratio of $2Δ_0/k_{\rm B}T_{\rm c}=2.74(1)$. The alternative nodal $p-$wave or $d-$wave scenarios with marginally worse goodness of fit would yield more realistic $2Δ_0/k_{\rm B}T_{\rm c}=3.50(2)$ and $2Δ_0/k_{\rm B}T_{\rm c}=4.08(1)$, respectively, and thus they cannot be ruled out when accounting for the superconducting state in Rb$_2$Mo$_3$As$_3$. △ Less

Submitted 6 February, 2023; originally announced February 2023.

Comments: 6 pages

Quantum spin liquid in the Ising triangular-lattice antiferromagnet neodymium heptatantalate

Authors: T. Arh, B. Sana, M. Pregelj, P. Khuntia, Z. Jagličić, M. D. Le, P. Biswas, A. Ozarowski, A. Zorko

Abstract: Disordered magnetic states known as spin liquids are of paramount importance in both fundamental and applied science. A classical state of this kind was predicted for the Ising antiferromagnetic triangular model more than half a century ago, while additional non-commuting exchange terms were proposed to induce its quantum version -- a quantum spin liquid. These predictions have not been yet confir… ▽ More Disordered magnetic states known as spin liquids are of paramount importance in both fundamental and applied science. A classical state of this kind was predicted for the Ising antiferromagnetic triangular model more than half a century ago, while additional non-commuting exchange terms were proposed to induce its quantum version -- a quantum spin liquid. These predictions have not been yet confirmed experimentally. Here we report a discovery of such a state in the structurally perfect triangular-lattice antiferromagnet NdTa$_7$O$_{19}$. Its magnetic ground state is characterized by spin-1/2 degrees of freedom with Ising-like interactions and gives rise to low-frequency spin excitations persisting down to the lowest temperatures. Our study demonstrates the key role of strong spin-orbit coupling in stabilizing spin liquids that result from magnetic anisotropy and highlights the large family of rare-earth (RE) heptatantalates RETa$_7$O$_{19}$ as a novel framework for realization of these states, which represent a promising platform for quantum applications. △ Less

Submitted 4 January, 2022; originally announced January 2022.

Comments: This is the initially submitted version of the manuscript, the considerably extended and revised published version is available online at https://doi.org/10.1038/s41563-021-01169-y

Journal ref: Nat. Mater. 21, 416 (2022)

Magnetic ordering of the distorted kagome antiferromagnet Y$_3$Cu$_9$(OH)$_{18}$[Cl$_8$(OH)] prepared via optimal synthesis

Authors: W. Sun, T. Arh, M. Gomilšek, P. Koželj, S. Vrtnik, M. Herak, J. -X. Mi, A. Zorko

Abstract: Experimental studies of high-purity kagome-lattice antiferromagnets (KAFM) are of great importance in attempting to better understand the predicted enigmatic quantum spin-liquid ground state of the KAFM model. However, realizations of this model can rarely evade magnetic ordering at low temperatures due to various perturbations to its dominant isotropic exchange interactions. Such a situation is f… ▽ More Experimental studies of high-purity kagome-lattice antiferromagnets (KAFM) are of great importance in attempting to better understand the predicted enigmatic quantum spin-liquid ground state of the KAFM model. However, realizations of this model can rarely evade magnetic ordering at low temperatures due to various perturbations to its dominant isotropic exchange interactions. Such a situation is for example encountered due to sizable Dzyaloshinskii-Moriya magnetic anisotropy in YCu$_3$(OH)$_6$Cl$_3$, which stands out from other KAFM materials by its perfect crystal structure. We find evidence of magnetic ordering also in the distorted sibling compound Y$_3$Cu$_9$(OH)$_{18}$[Cl$_8$(OH)], which has recently been proposed to feature a spin-liquid ground state arising from a spatially anisotropic kagome lattice. Our findings are based on a combination of bulk susceptibility, specific heat, and magnetic torque measurements that disclose a Néel transition temperature of $T_N=11$~K in this material, which might feature a coexistence of magnetic order and persistent spin dynamics as previously found in YCu$_3$(OH)$_6$Cl$_3$. Contrary to previous studies of single crystals and powders containing impurity inclusions, we use high-purity single crystals of Y$_3$Cu$_9$(OH)$_{18}$[Cl$_8$(OH)] grown via an optimized hydrothermal synthesis route that minimizes such inclusions. This study thus demonstrates that the lack of magnetic ordering in less pure samples of the investigated compound does not originate from the reduced symmetry of spin lattice but is instead of extrinsic origin. △ Less

Submitted 20 May, 2021; v1 submitted 24 March, 2021; originally announced March 2021.

Journal ref: Phys. Rev. Materials 5, 064401 (2021)

Development of short and long-range magnetic order in the double perovskite based frustrated triangular lattice antiferromagnet Ba2MnTeO6

Authors: J. Khatua, T. Arh, Shashi B. Mishra, H. Luetkens, A. Zorko, B. Sana, M. S. Ramachandra Rao, B. R. K. Nanda, P. Khuntia

Abstract: Oxide double perovskites wherein octahedra formed by both 3d elements and sp-based heavy elements give rise to unconventional magnetic ordering and correlated quantum phenomena crucial for futuristic applications. Here, by carrying out experimental and first principles investigations, we present the electronic structure and magnetic phases of Ba2MnTeO6, where Mn^2+ ions with S = 5/2 spins constitu… ▽ More Oxide double perovskites wherein octahedra formed by both 3d elements and sp-based heavy elements give rise to unconventional magnetic ordering and correlated quantum phenomena crucial for futuristic applications. Here, by carrying out experimental and first principles investigations, we present the electronic structure and magnetic phases of Ba2MnTeO6, where Mn^2+ ions with S = 5/2 spins constitute a perfect triangular lattice. The magnetic susceptibility reveals a large Curie- Weiss temperature -152 K suggesting the presence of strong antiferromagnetic interactions between Mn^2+ moments in the spin lattice. A phase transition at 20 K is revealed by magnetic susceptibility and specific heat which is attributed to the presence of a sizeable inter-plane interactions. Below the transition temperature, the specific heat data show antiferromagnetic magnon excitations with a gap of 1.4 K. Furthermore, muon spin-relaxation reveals the presence of static internal fields in the ordered state and provides strong evidence of short-range spin correlations for T > TN. The DFT+U calculations and spin-dimer analysis infer that Heisenberg interactions govern the inter and intra-layer spin-frustrations in this perovskite. The inter and intra-layer exchange interactions are of comparable strengths (J1 = 4.6 K, J2 = 0.92 J1). However, a weak third nearest-neighbor ferromagnetic inter-layer interaction exists (J3=-0.04 J1) due to double-exchange interaction via the linear path Mn-O-Te-O-Mn. The combined effect of J2 and J3 interactions stabilizes a three dimensional long-range magnetic ordering in this frustrated magnet. △ Less

Submitted 21 December, 2020; originally announced December 2020.

Journal ref: Scientific Reports 11, 6959 (2021)

Dynamical spin correlations of the kagome antiferromagnet

Authors: P. Prelovšek, M. Gomilšek, T. Arh, A. Zorko

Abstract: Temperature-dependent dynamical spin correlations, which can be readily accessed via a variety of experimental techniques, hold the potential of offering a unique fingerprint of quantum spin liquids and other intriguing dynamical states. In this work we present an in-depth study of the temperature-dependent dynamical spin structure factor $S({\bf q}, ω)$ of the antiferromagnetic (AFM) Heisenberg s… ▽ More Temperature-dependent dynamical spin correlations, which can be readily accessed via a variety of experimental techniques, hold the potential of offering a unique fingerprint of quantum spin liquids and other intriguing dynamical states. In this work we present an in-depth study of the temperature-dependent dynamical spin structure factor $S({\bf q}, ω)$ of the antiferromagnetic (AFM) Heisenberg spin-1/2 model on the kagome lattice with additional Dzyaloshinskii--Moriya (DM) interactions. Using the finite-temperature Lanczos method on lattices with up to $N = 30$ sites we find that even without DM interactions, chiral low-energy spin fluctuations of the $120^\circ$ AFM order parameter dominate the dynamical response. This leads to a nontrivial frequency dependence of $S({\bf q}, ω)$ and the appearance of a pronounced low-frequency mode at the M point of the extended Brillouin zone. Adding an out-of-plane DM interactions $D^z$ gives rise to an anisotropic dynamical response, a softening of in-plane spin fluctuations, and, ultimately, the onset of a coplanar AFM ground-state order at $D^z > 0.1 J$. Our results are in very good agreement with existing inelastic neutron scattering and temperature-dependent NMR spin-lattice relaxation rate ($1/T_1$) data on the paradigmatic kagome AFM herbertsmithite, where the effect of its small $D^z$ on the dynamical spin correlations is shown to be rather small, as well as with $1/T_1$ data on the novel kagome AFM YCu$_3$(OH)$_6$Cl$_3$, where its substantial $D^z \approx 0.25 J$ interaction is found to strongly affect the spin dynamics. △ Less

Submitted 20 January, 2021; v1 submitted 4 November, 2020; originally announced November 2020.

Journal ref: Phys. Rev. B 103, 014431 (2021)

Superconductivity in the regime of attractive interactions in the Tomonaga-Luttinger liquid

Authors: Ž. Gosar, N. Janša, T. Arh, P. Jeglič, M. Klanjšek, H. F. Zhai, B. Lv, D. Arčon

Abstract: While the vast majority of known physical realizations of the Tomonaga-Luttinger liquid (TLL) have repulsive interactions defined with the dimensionless interaction parameter $K_{\rm c}<1$, we here report that Rb$_2$Mo$_3$As$_3$ is in the opposite TLL regime of attractive interactions. This is concluded from a TLL-characteristic power-law temperature dependence of the $^{87}$Rb spin-lattice relaxa… ▽ More While the vast majority of known physical realizations of the Tomonaga-Luttinger liquid (TLL) have repulsive interactions defined with the dimensionless interaction parameter $K_{\rm c}<1$, we here report that Rb$_2$Mo$_3$As$_3$ is in the opposite TLL regime of attractive interactions. This is concluded from a TLL-characteristic power-law temperature dependence of the $^{87}$Rb spin-lattice relaxation rates over broad temperature range yielding the TLL interaction parameter for charge collective modes $K_{\rm c}=1.4$. The TLL of the one-dimensional band can be traced almost down to $T_{\rm c} = 10.4 $~K, where the bulk superconducting state is stabilized by the presence of a three-dimensional band and characterized by the $^{87}$Rb temperature independent Knight shift and the absence of Hebel-Slichter coherence peak in the relaxation rates. The small superconducting gap measured in high magnetic fields reflects either the importance of the vortex core relaxation or the uniqueness of the superconducting state stemming from the attractive interactions defining the precursor TLL. △ Less

Submitted 22 June, 2020; v1 submitted 22 January, 2020; originally announced January 2020.

Comments: 6 pages, 4 figures. 5 figures and one table in supplemental material

Journal ref: Phys. Rev. B 101, 220508 (2020)

Origin of Magnetic Ordering in a Structurally-Perfect Quantum Kagome Antiferromagnet

Authors: T. Arh, M. Gomilšek, P. Prelovšek, M. Pregelj, M. Klanjšek, A. Ozarowski, S. J. Clark, T. Lancaster, W. Sun, J. -X. Mi, A. Zorko

Abstract: The ground state of the simple Heisenberg nearest-neighbor quantum kagome antiferromagnetic model is a magnetically disordered spin liquid, yet various perturbations may lead to fundamentally different states. Here we disclose the origin of magnetic ordering in the structurally-perfect kagome material YCu$_3$(OH)$_6$Cl$_3$, which is free of the widespread impurity problem. {\it Ab-initio} calculat… ▽ More The ground state of the simple Heisenberg nearest-neighbor quantum kagome antiferromagnetic model is a magnetically disordered spin liquid, yet various perturbations may lead to fundamentally different states. Here we disclose the origin of magnetic ordering in the structurally-perfect kagome material YCu$_3$(OH)$_6$Cl$_3$, which is free of the widespread impurity problem. {\it Ab-initio} calculations and modeling of its magnetic susceptibility reveal that, similar to the archetypal case of herbertsmithite, the nearest-neighbor exchange is by far the dominant isotropic interaction. Dzyaloshinskii-Moriya (DM) magnetic anisotropy deduced from electron spin resonance and specific-heat measurements is, however, significantly larger than in herbertsmithite. By enhancing spin correlations within kagome planes, this anisotropy is essential for magnetic ordering. Our study isolates the effect of DM anisotropy from other perturbations and unambiguously confirms the theoretical phase diagram. △ Less

Submitted 9 July, 2020; v1 submitted 19 December, 2019; originally announced December 2019.

Comments: Manuscript plus Supplemental Information

Journal ref: Phys. Rev. Lett. 125, 027203 (2020)

Emission of correlated jets from a driven matter-wave soliton in a quasi-one-dimensional geometry

Authors: Tadej Mežnaršič, Rok Žitko, Tina Arh, Katja Gosar, Erik Zupanič, Peter Jeglič

Abstract: We demonstrate the emission of correlated atom jets from a matter-wave soliton in a quasi-one-dimensional optical trap. We characterize the dependence of jet properties on the frequency, amplitude and length of the modulation, and qualitatively reproduce the trends in the mean-field picture with a one-dimensional time-dependent Gross-Pitaevskii equation simulation. High-order jets are observed for… ▽ More We demonstrate the emission of correlated atom jets from a matter-wave soliton in a quasi-one-dimensional optical trap. We characterize the dependence of jet properties on the frequency, amplitude and length of the modulation, and qualitatively reproduce the trends in the mean-field picture with a one-dimensional time-dependent Gross-Pitaevskii equation simulation. High-order jets are observed for sufficiently long pulses. A double-pulse modulation sequence produces consecutive jets, and a multi-pulse sequence may lead to irregular 3D jets at a finite angle to the direction of the channel. In the limit of vanishing high-order jets beyond-mean-field number correlations of jet pairs are demonstrated, implying possible number squeezing. △ Less

Submitted 7 April, 2020; v1 submitted 24 May, 2019; originally announced May 2019.

Comments: 5 pages, 4 figures, published in PRA

Journal ref: Phys. Rev. A 101, 031601 (2020)

Cesium bright matter-wave solitons and soliton trains

Authors: Tadej Mežnaršič, Tina Arh, Jure Brence, Jaka Pišljar, Katja Gosar, Žiga Gosar, Rok Žitko, Erik Zupanič, Peter Jeglič

Abstract: A study of bright matter-wave solitons of a cesium Bose-Einstein condensate (BEC) is presented. Production of a single soliton is demonstrated and dependence of soliton atom number on the interatomic interaction is investigated. Formation of soliton trains in the quasi one-dimensional confinement is shown. Additionally, fragmentation of a BEC has been observed outside confinement, in free space. I… ▽ More A study of bright matter-wave solitons of a cesium Bose-Einstein condensate (BEC) is presented. Production of a single soliton is demonstrated and dependence of soliton atom number on the interatomic interaction is investigated. Formation of soliton trains in the quasi one-dimensional confinement is shown. Additionally, fragmentation of a BEC has been observed outside confinement, in free space. In the end a double BEC production setup for studying soliton collisions is described. △ Less

Submitted 5 March, 2019; v1 submitted 8 February, 2019; originally announced February 2019.

Comments: 9 pages, 7 figures, accepted for publication in Phys. Rev. A

Journal ref: Phys. Rev. A 99, 033625 (2019)