121 research outputs found
Signatures of a gearwheel quantum spin liquid in a spin- pyrochlore molybdate Heisenberg antiferromagnet
We theoretically investigate the low-temperature phase of the recently
synthesized LuMoON material, an extraordinarily rare
realization of a three-dimensional pyrochlore Heisenberg
antiferromagnet in which Mo are the magnetic species. Despite a
Curie-Weiss temperature () of K, experiments have
found no signature of magnetic ordering spin freezing down to
K. Using density functional theory, we find that the compound
is well described by a Heisenberg model with exchange parameters up to third
nearest neighbors. The analysis of this model via the pseudofermion functional
renormalization group method reveals paramagnetic behavior down to a
temperature of at least , in agreement with the
experimental findings hinting at a possible three-dimensional quantum spin
liquid. The spin susceptibility profile in reciprocal space shows
momentum-dependent features forming a "gearwheel" pattern, characterizing what
may be viewed as a molten version of a chiral noncoplanar incommensurate spiral
order under the action of quantum fluctuations. Our calculated reciprocal space
susceptibility maps provide benchmarks for future neutron scattering
experiments on single crystals of LuMoON.Comment: Published version. Main paper (6 pages, 3 figures) + Supplemental
Material (4 pages, 3 figures, 1 table
First principles studies of frustrated spin systems: from low-energy models to experiments
In this thesis, we presented the theoretical description of the magnetic properties of various frustrated spin systems. Especially in search of exotic states, such as quantum spin liquids, magnetically frustrated systems have been subject of intense research within the last four decades. Relating experimental observations in real materials with theoretical models that capture those exotic magnetic phenomena has been one of the great challenges within the field of magnetism in condensed matter.
In order to build such a bridge between experimental observations and theoretical models, we followed two complementary strategies in this thesis. One strategy was based on first principles methods that enable the theoretical prediction of electronic properties of real materials without further experimental input than the crystal structure. Based on these predictions, low-energy models that describe magnetic interactions can be extracted and, through further theoretical modelling, can be compared to experimental observations. The second strategy was to establish low-energy models through comparison of data from experiments, such as inelastic neutron scattering intensities, with calculated predictions based on a variety of plausible magnetic models guided by microscopic insights. Both approaches allow to relate theoretical magnetic models with real materials and may provide guidance for the design of new frustrated materials or the investigation of promising models related to exotic magnetic states
Ingredients for Generalized Models of <i>κ</i>-Phase Organic Charge-Transfer Salts: A Review
The families of organic charge-transfer salts κ-(BEDT-TTF)2X and κ-(BETS)2X, where BEDT-TTF and BETS stand for the organic donor molecules C10H8S8 and C10H8S4Se4, respectively, and X for an inorganic electron acceptor, have been proven to serve as a powerful playground for the investigation of the physics of frustrated Mott insulators. These materials have been ascribed a model character, since the dimerization of the organic molecules allows to map these materials onto a single band Hubbard model, in which the dimers reside on an anisotropic triangular lattice. By changing the inorganic unit X or applying physical pressure, the correlation strength and anisotropy of the triangular lattice can be varied. This has led to the discovery of a variety of exotic phenomena, including quantum-spin liquid states, a plethora of long-range magnetic orders in proximity to a Mott metal-insulator transition, and unconventional superconductivity. While many of these phenomena can be described within this effective one-band Hubbard model on a triangular lattice, it has become evident in recent years that this simplified description is insufficient to capture all observed magnetic and electronic properties. The ingredients for generalized models that are relevant include, but are not limited to, spin-orbit coupling, intra-dimer charge and spin degrees of freedom, electron-lattice coupling, as well as disorder effects. Here, we review selected theoretical and experimental discoveries that clearly demonstrate the relevance thereof. At the same time, we outline that these aspects are not only relevant to this class of organic charge-transfer salts, but are also receiving increasing attention in other classes of inorganic strongly correlated electron systems. This reinforces the model character that the κ-phase organic charge-transfer salts have for understanding and discovering novel phenomena in strongly correlated electron systems from a theoretical and experimental point of view
Ingredients for Generalized Models of κ-Phase Organic Charge-Transfer Salts: A Review
The families of organic charge-transfer salts κ-(BEDT-TTF)2X and κ-(BETS)2X, where BEDT-TTF and BETS stand for the organic donor molecules C10H8S8 and C10H8S4Se4, respectively, and X for an inorganic electron acceptor, have been proven to serve as a powerful playground for the investigation of the physics of frustrated Mott insulators. These materials have been ascribed a model character, since the dimerization of the organic molecules allows to map these materials onto a single band Hubbard model, in which the dimers reside on an anisotropic triangular lattice. By changing the inorganic unit X or applying physical pressure, the correlation strength and anisotropy of the triangular lattice can be varied. This has led to the discovery of a variety of exotic phenomena, including quantum-spin liquid states, a plethora of long-range magnetic orders in proximity to a Mott metal-insulator transition, and unconventional superconductivity. While many of these phenomena can be described within this effective one-band Hubbard model on a triangular lattice, it has become evident in recent years that this simplified description is insufficient to capture all observed magnetic and electronic properties. The ingredients for generalized models that are relevant include, but are not limited to, spin-orbit coupling, intra-dimer charge and spin degrees of freedom, electron-lattice coupling, as well as disorder effects. Here, we review selected theoretical and experimental discoveries that clearly demonstrate the relevance thereof. At the same time, we outline that these aspects are not only relevant to this class of organic charge-transfer salts, but are also receiving increasing attention in other classes of inorganic strongly correlated electron systems. This reinforces the model character that the κ-phase organic charge-transfer salts have for understanding and discovering novel phenomena in strongly correlated electron systems from a theoretical and experimental point of view
Critical spin liquid versus valence-bond glass in a triangular-lattice organic antiferromagnet
In the quest for materials with unconventional quantum phases, the organic triangular-lattice antiferromagnet κ-(ET)2Cu2(CN)3 has been extensively discussed as a quantum spin liquid (QSL) candidate. The description of its low temperature properties has become, however, a particularly challenging task. Recently, an intriguing quantum critical behaviour was suggested from low-temperature magnetic torque experiments. Here we highlight significant deviations of the experimental observations from a quantum critical scenario by performing a microscopic analysis of all anisotropic contributions, including Dzyaloshinskii–Moriya and multi-spin scalar chiral interactions. Instead, we show that disorder-induced spin defects provide a comprehensive explanation of the low-temperature properties. These spins are attributed to valence bond defects that emerge spontaneously as the QSL enters a valence-bond glass phase at low temperature. This theoretical treatment is applicable to a general class of frustrated magnetic systems and has important implications for the interpretation of magnetic torque, nuclear magnetic resonance, thermal transport and thermodynamic experiments
Probing α
Recent studies have brought -RuCl to the forefront of
experimental searches for materials realizing Kitaev spin-liquid physics. This
material exhibits strongly anisotropic exchange interactions afforded by the
spin-orbit coupling of the 4d Ru centers. We investigate the dynamical response
at finite temperature and magnetic field for a realistic model of the magnetic
interactions in -RuCl. These regimes are thought to host
unconventional paramagnetic states that emerge from the suppression of magnetic
order. Using exact diagonalization calculations of the quantum model
complemented by semi-classical analysis, we find a very rich evolution of the
spin dynamics as the applied field suppresses the zigzag order and stabilizes a
quantum paramagnetic state that is adiabatically connected to the fully
polarized state at high fields. At finite temperature, we observe large
redistributions of spectral weight that can be attributed to the anisotropic
frustration of the model. These results are compared to recent experiments, and
provide a roadmap for further studies of these regimes.Comment: final published version; 5 pages, 4 figures + supplementa
- …