المؤلفون: Bachhar, Sanjay, Baenitz, M., Luetkens, Hubertus, Pujari, Sumiran, Mahajan, A. V.

مصطلحات موضوعية: Condensed Matter - Strongly Correlated Electrons

الوصف: We report the synthesis and properties of (H,Li)$_{6}$Ru$_{2}$O$_{6}$, which is shown to be a $J_{\text{eff}}=\frac{1}{2}$ system made out of Ru$^{3+}$ moments in a honeycomb geometry. Bulk magnetization, heat capacity, nuclear magnetic resonance (NMR), and muon spin relaxation ($\mu$SR) rule out the presence of static moments or any spin glass phase down to 500 mK. All techniques suggest a crossover to a liquid-like state below about 40 K. The $^{7}$Li nuclear magnetic resonance (NMR) shift data suggest a non-zero $T$-independent spin susceptibility at low $T$. In zero field, $C_m/T$ shows $T^{-1}$ divergence which is consistent with vacancy-induced effects on low-energy excitations of the pristine Kitaev spin liquid. With field, power-law variations in the $^{7}$Li NMR spin-lattice relaxation rate 1/T$_{1}$ and magnetic heat capacity $C_{m}$ show quantitatively new scaling behaviors. A two-step entropy release in heat capacity is also observed putatively from $Z_{2}$ flux (low-$T$ step) and itinerant Majorana fermions (high-$T$ step). Based on these findings, we propose that (H,Li)$_{6}$Ru$_{2}$O$_{6}$ realizes a Kitaev spin liquid with no evidence of inherent magnetic ordering in zero field unlike $\alpha$-RuCl$_{3}$ where approximately $8$ Tesla field is required to suppress magnetic order.
Comment: 5 pages, 6 figures of main text + 12 pages, 25 figures of supplementary information

URL الوصول: http://arxiv.org/abs/2405.06380

المؤلفون: Fujii, T., Janson, O., Yasuoka, H., Rosner, H., Prots, Yu., Burkhardt, U., Schmidt, M., Baenitz, M.

المصدر: Phys. Rev. B 109, 035116 (2024)

مصطلحات موضوعية: Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science

الوصف: The local electric field gradients and magnetic dynamics of TaSb$_2$ have been studied using $^{121}$Sb, $^{123}$Sb, and $^{181}$Ta nuclear quadrupole resonance (NQR) with density functional theory (DFT) calculations using XRD-determined crystal structures. By measuring all structurally expected thirteen NQR lines, the nuclear quadrupole coupling constant ($\nu_Q$) and asymmetric parameter ($\eta$) for Ta, Sb(1), and Sb(2) sites were obtained. These values are all in good agreement with the presented DFT calculations. Principal axes of the electric field gradients was determined for a single-crystal sample by measuring the angular dependencies of NMR frequency under a weak magnetic field. The unusual temperature dependence of $\eta$(T) of Sb(2) hints at the suppressed thermal expansion along the $a$-axis. Spin lattice relaxation rate ($1/T_1T$) measurements reveal an activated-type behavior and an upturn below 30 K. Neither the low temperature upturn nor the high temperature activation type behaviors are reproduced by the calculated $1/T_1T$ based on the calculated density of states (DOS). On the other hand, the agreement between the calculated DOS and specific heat measurements indicates that the band renormalization is small. This fact indicates that TaSb$_2$ deviates from the simple semimetal scenario, and magnetic excitations are not captured by Fermi liquid theory.
Comment: 15 pages, 13 figures

URL الوصول: http://arxiv.org/abs/2312.11007

المؤلفون: Islam, S. S., Mukharjee, Prashanta K., Biswas, P. K., Telling, Mark, Skourski, Y., Ranjith, K. M., Baenitz, M., Inagaki, Y., Furukawa, Y., Tsirlin, A. A., Nath, R.

مصطلحات موضوعية: Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science

الوصف: We probe the magnetic field-induced Tomonaga-Luttinger liquid (TLL) state in the bond-alternating spin-$1/2$ antiferromagnetic (AFM) chain compound NaVOPO$_4$ using thermodynamic as well as local $\mu$SR and $^{31}$P NMR probes down to milli-K temperatures in magnetic fields up to 14~T. The $\mu$SR and NMR relaxation rates in the gapless TLL regime decay slowly following characteristic power-law behaviour, enabling us to directly determine the interaction parameter $K$ as a function of the magnetic field. These estimates are cross-checked using magnetization and specific heat data. The field-dependent $K$ lies in the range of $0.4 < K < 1$ and indicates repulsive nature of interactions between the spinless fermions, in line with the theoretical predictions. This renders NaVOPO$_4$ the first experimental realization of TLL with repulsive fermionic interactions in hitherto studied $S=1/2$ bond-alternating AFM-AFM chain compounds.
Comment: 7 pages, 2 figures, 47 references

URL الوصول: http://arxiv.org/abs/2311.03231

المؤلفون: Khatua, J., Sana, B., Zorko, A., Gomilšek, M., Rao, K. Sethupathi M. S. Ramachandra, Baenitz, M., Schmidt, B., Khuntia, P.

المصدر: Physics Reports 1041, 1 (2023)

مصطلحات موضوعية: Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science, Quantum Physics

الوصف: Frustration in magnetic materials arising from competing exchange interactions can prevent the system from adopting long-range magnetic order and can instead lead to a diverse range of novel quantum and topological states with exotic quasiparticle excitations. Here, we review prominent examples of such emergent phenomena, including magnetically-disordered and extensively degenerate spin ices, which feature emergent magnetic monopole excitations, highly-entangled quantum spin liquids with fractional spinon excitations, topological order and emergent gauge fields, as well as complex particle-like topological spin textures known as skyrmions. We provide an overview of recent advances in the search for magnetically-disordered candidate materials on the three-dimensional pyrochlore lattice and two-dimensional triangular, kagome and honeycomb lattices, the latter with bond-dependent Kitaev interactions, and on lattices supporting topological magnetism. We highlight experimental signatures of these often elusive phenomena and single out the most suitable experimental techniques that can be used to detect them. Our review also aims at providing a comprehensive guide for designing and investigating novel frustrated magnetic materials, with the potential of addressing some important open questions in contemporary condensed matter physics.

URL الوصول: http://arxiv.org/abs/2310.15071

المؤلفون: Sichelschmidt, Jörg, Häußler, Ellen, Vinokurova, Ekaterina, Baenitz, M., Doert, Thomas

المصدر: J. Phys.: Condens. Matter 35, 425601 (2023)

مصطلحات موضوعية: Condensed Matter - Strongly Correlated Electrons

الوصف: The local magnetic properties of Yb$^{3+}$ in the layered honeycomb material YbCl$_{3}$ were investigated by electron spin resonance on single crystals. For in-plane and out-of-plane field orientations the $g$-factor shows a clear anisotropy ($g_\|=2.97(8)$ and $g_\bot =1.53(4)$), whereas the low temperature exchange coupling and the spin relaxation display a rather isotropic character. At elevated temperatures the contribution of the first excited crystal field level ($21\pm2$~meV) dominates the spin relaxation.
Comment: 10 pages, 5 figures

URL الوصول: http://arxiv.org/abs/2307.09335

المؤلفون: Mohanty, S., Islam, S. S., Winterhalter-Stocker, N., Jesche, A., Simutis, G., Wang, Ch., Guguchia, Z., Sichelschmidt, J., Baenitz, M., Tsirlin, A. A., Gegenwart, P., Nath, R.

مصطلحات موضوعية: Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science

الوصف: We delineate quantum magnetism in the strongly spin-orbit coupled, distorted honeycomb-lattice antiferromagnet BiYbGeO$_{5}$. Our magnetization and heat capacity measurements reveal that its low-temperature behavior is well described by an effective $J_{\rm eff}=1/2$ Kramers doublet of Yb$^{3+}$. The ground state is nonmagnetic with a tiny spin gap. Temperature-dependent magnetic susceptibility, magnetization isotherm, and heat capacity could be modeled well assuming isolated spin dimers with anisotropic exchange interactions $J_{\rm Z} \simeq 2.6$~K and $J_{\rm XY} \simeq 1.3$~K. Heat capacity measurements backed by muon spin relaxation suggest the absence of magnetic long-range order down to at least 80\,mK both in zero field and in applied fields. This sets BiYbGeO$_5$ apart from Yb$_2$Si$_2$O$_7$ with its unusual regime of magnon Bose-Einstein condensation and suggests negligible interdimer couplings, despite only a weak structural deformation of the honeycomb lattice.
Comment: 6 pages, 5 figures

URL الوصول: http://arxiv.org/abs/2305.10221

المؤلفون: Sana, B., Barik, M., Lee, S., Jena, U., Baenitz, M., Sichelschmidt, J., Luther, S., Kuehne, H., Sethupathi, K., Rao, M. S. Ramachandra, Choi, K. Y., Khuntia, P.

مصطلحات موضوعية: Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science

الوصف: Collective behavior of spins, frustration-induced strong quantum fluctuations and subtle interplay between competing degrees of freedom in quantum materials can lead to correlated quantum states with fractional excitations that are essential ingredients for establishing paradigmatic models and have immense potential for quantum technologies. Quenched randomness is a new paradigm in elucidating the emergence of spin-liquidlike states in geometrically frustrated magnets. Herein, we report magnetization, specific heat, electron spin resonance, and muon spin resonance studies on a 3d-electron-based square lattice antiferromagnet Sr3CuTa2O9. In this material, S = 1/2 Cu2+ nearest-neighbor ions constitute a two-dimensional square lattice. The negative value of Curie-Weiss temperature, obtained from the Curie-Weiss fit of high-temperature magnetic susceptibility data indicates the presence of antiferromagnetic interaction between Cu2+ moments. Specific heat data show the absence of long-range magnetic ordering down to 64 mK despite a reasonably strong exchange interaction between Cu2+ spins as reflected from a Curie-Weiss temperature of -27 K. The power-law behavior and the data collapse of specific heat and magnetization data evince the emergence of a random-singlet state in Sr3CuTa2O9. The power-law-like spin auto-correlation function and the data collapse of muon polarization asymmetry with longitudinal field dependence of t/({\mu}0H){\gamma} further support credence to the presence of a randomness-induced liquid-like state. Our results suggest that randomness induced by disorder is a viable route to realize quantum spin liquid-like state in this square lattice antiferromagnet.

URL الوصول: http://arxiv.org/abs/2304.13116

المؤلفون: Sana, B., Barik, M., Pregelj, M., Jena, U., Baenitz, M., Sichelschmidt, J., Sethupathi, K., Khuntia, P.

المصدر: Physical Review B 108, 134413 (2023)

مصطلحات موضوعية: Condensed Matter - Strongly Correlated Electrons

الوصف: The interplay between competing degrees of freedom can stabilize non-trivial magnetic states in correlated electron materials. Frustration-induced strong quantum fluctuations can evade long-range magnetic ordering leading to exotic quantum states such as spin liquids in two-dimensional spin-lattices such as triangular and kagome structures. However, the experimental realization of dynamic and correlated quantum states is rare in three-dimensional (3D) frustrated magnets wherein quantum fluctuations are less prominent. Herein, we report the crystal structure, magnetic susceptibility, electron spin resonance (ESR) and specific heat studies accompanied by crystal electric field (CEF) calculations on a 3D frustrated magnet Yb3Sc2Ga3O12. In this material, Yb3+ ions form a three-dimensional network of corner-sharing triangles known as hyperkagome lattice without any detectable anti-site disorder. Our results reveal a low energy state with Jeff = 1/2 degrees of freedom in the Kramers doublet state. The zero field-cooled and field cooled magnetic susceptibility taken in 0.001 T rules out the presence of spin-freezing down to 1.8K. The Curie-Weiss (CW) fit to low-T susceptibility data yields a small and negative CW temperature indicating the presence of a weak antiferromagnetic interaction between Jeff = 1/2 (Yb3+) moments. The Yb-ESR displays a broad line of non-Lorentzian shape that suggests considerable magnetic anisotropy in Yb3Sc2Ga3O12. The CEF calculations suggest that the ground state is well separated from the excited states, which are in good agreement with experimental results. The absence of long-range magnetic ordering indicates a dynamic liquid-like ground state at least down to 130 mK. Furthermore, zero field specific heat shows a broad maximum around 200 mK suggesting the presence of short-range spin correlations in this 3D frustrated antiferromagnet.

URL الوصول: http://arxiv.org/abs/2304.07350

المؤلفون: Somesh, K., Islam, S. S., Mohanty, S., Simutis, G., Guguchia, Z., Wang, Ch., Sichelschmidt, J., Baenitz, M., Nath, R.

مصطلحات موضوعية: Condensed Matter - Strongly Correlated Electrons, Condensed Matter - Materials Science

الوصف: We present the ground state properties of a new quantum antiferromagnet YbBO$_3$ in which the isotropic Yb$^{3+}$ triangular layers are separated by a non-magnetic layer of partially occupied B and O(2) sites. The magnetization and heat capacity data establish a spin-orbit entangled effective spin $J_{\rm eff} = 1/2$ state of Yb$^{3+}$ ions at low temperatures, interacting antiferromagnetically with an intra-layer coupling $J/k_{\rm B} \simeq 0.53$ K. The absence of oscillations and a $1/3$ tail in the zero-field muon asymmetries rule out the onset of magnetic long-range-order as well as spin-freezing down to 20~mK. An anomalous broad maximum in the temperature dependent heat capacity with a unusually reduced value and a broad anomaly in zero-field muon depolarization rate centered at $T^*\simeq 0.7 \frac{J}{k_{\rm B}}$ provide compelling evidence for a wide fluctuating regime ($0.182 \leq T/J \leq 1.63$) with slow relaxation. We infer that the fluctuating regime is a universal feature of a highly frustrated triangular lattice antiferromagnets while the absence of magnetic long-range-order is due to perfect two-dimensionality of the spin-lattice protected by non-magnetic site disorder.
Comment: 7 pages, 4 figures

URL الوصول: http://arxiv.org/abs/2210.09724

المؤلفون: Opherden, D., Tepaske, M. S. J., Bärtl, F., Weber, M., Turnbull, M. M., Lancaster, T., Blundell, S. J., Baenitz, M., Wosnitza, J., Landee, C. P., Moessner, R., Luitz, D. J., Kühne, H.

مصطلحات موضوعية: Condensed Matter - Strongly Correlated Electrons

الوصف: We report the manifestation of field-induced Berezinskii-Kosterlitz-Thouless (BKT) correlations in the weakly coupled spin-1/2 Heisenberg layers of the molecular-based bulk material [Cu(pz)$_2$(2-HOpy)$_2$](PF$_6$)$_2$. Due to the moderate intralayer exchange coupling of $J/k_\mathrm{B} = 6.8$ K, the application of laboratory magnetic fields induces a substantial $XY$ anisotropy of the spin correlations. Crucially, this provides a significant BKT regime, as the tiny interlayer exchange $J^\prime / k_\mathrm{B} \approx 1$ mK only induces 3D correlations upon close approach to the BKT transition with its exponential growth in the spin-correlation length. We employ nuclear magnetic resonance and $\mu^{+}$SR measurements to probe the spin correlations that determine the critical temperatures of the BKT transition as well as that of the onset of long-range order. Further, we perform stochastic series expansion quantum Monte Carlo simulations based on the experimentally determined model parameters. Finite-size scaling of the in-plane spin stiffness yields excellent agreement of critical temperatures between theory and experiment, providing clear evidence that the nonmonotonic magnetic phase diagram of [Cu(pz)$_2$(2-HOpy)$_2$](PF$_6$)$_2$ is determined by the field-tuned $XY$ anisotropy and the concomitant BKT physics.
Comment: 10 pages, 7 figures

URL الوصول: http://arxiv.org/abs/2209.11085