16 results on '"Katsuhiro Morita"'
Search Results
2. Effects of bond-randomness and Dzyaloshinskii-Moriya interactions on the specific heat at low temperatures of a spherical kagomé cluster in {W$_{72}$V$_{30}$}
- Author
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Mikio Motohashi, Kouki Inoue, Katsuhiro Morita, Yoshiyuki Fukumoto, and Hiroki Nakano
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Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,General Physics and Astronomy ,FOS: Physical sciences ,Condensed Matter::Strongly Correlated Electrons - Abstract
For the spin-1/2 spherical kagomé cluster, as well as for the 2D kagomé lattice, many low-energy singlet excitations have been expected to exist in the energy region below the spin gap, which has been actually confirmed by Kihara et al. in their specific heat measurements up to 10 K in {W72V30}, for which the exchange interaction was estimated as J = 115 K. However, the experimental result of the specific heat cannot be reproduced by the theoretical result in the Heisenberg model. Although the theoretical result has a peak around 2 K, the experimental one does not. To elucidate this difference, we incorporate Dzyaloshinskii–Moriya (DM) interactions and bond-randomness into the model Hamiltonian for {W72V30} and calculate the density of states, entropy, and specific heat at low temperatures by using the Lanczos method. We find that DM interactions do not significantly affect the energy distribution of about 10 singlet states above the ground state, which are involved in the peak structure of the specific heat around 2 K, while even 10% bond-randomness disperses this distribution to collapse the 2 K peak. Kihara et al. also reported experimental specific heats under magnetic fields up to 15 T (= 0.17J), and found that the specific heats show almost no magnetic field dependence, which strongly suggests that the bond-randomness is much stronger than the magnetic fields. For example, our calculated specific heats with 50% randomness reproduce the experimental ones up to about 5 K.
- Published
- 2021
- Full Text
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3. Isothermal and adiabatic magnetization processes of the spin-$\frac{1}{2}$ Heisenberg model on an anisotropic triangular lattice
- Author
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Katsuhiro Morita
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,FOS: Physical sciences - Abstract
In this study, we investigate the magnetic susceptibility, entropy, and isothermal magnetization curve of the spin-1/2 Heisenberg model on an anisotropic triangular lattice using the orthogonalized finite-temperature Lanczos method. In addition, we investigate the adiabatic magnetization curve and magnetocaloric effect. We estimate these physical quantities with sufficient accuracy in the thermodynamic limit, except at low temperatures. We observe a 1/3 magnetization plateau in the isothermal magnetization process, whereas the plateau is observed to have a slope in the adiabatic process. We show that the magnetocaloric effect can be used to detect the signature of phase transitions. We believe that these results will be useful for understanding the magnetism of anisotropic triangular lattice compounds through a comparison with experimental results in the future.
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- 2021
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4. Resonating dimer-monomer liquid state in a magnetization plateau of a spin-$\frac{1}{2}$ kagome-strip Heisenberg chain
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Shigetoshi Sota, Takami Tohyama, and Katsuhiro Morita
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Computer Science::Machine Learning ,media_common.quotation_subject ,Lattice (group) ,General Physics and Astronomy ,Frustration ,FOS: Physical sciences ,02 engineering and technology ,Quantum entanglement ,Spin structure ,Computer Science::Digital Libraries ,01 natural sciences ,Statistics::Machine Learning ,Condensed Matter - Strongly Correlated Electrons ,0103 physical sciences ,010306 general physics ,Spin-½ ,media_common ,Physics ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Heisenberg model ,Density matrix renormalization group ,021001 nanoscience & nanotechnology ,Computer Science::Mathematical Software ,Condensed Matter::Strongly Correlated Electrons ,Quantum spin liquid ,0210 nano-technology - Abstract
Highly frustrated spin systems such as the kagome lattice are a treasure trove of new quantum states with large entanglements. Herein, we study the spin-$$\frac{1}{2}$$ 1 2 Heisenberg model on a kagome-strip chain, which is a one-dimensional kagome lattice, using the density matrix renormalization group method. Calculating the central charge and entanglement spectrum for the kagome-strip chain, we find a gapless spin liquid state with doubly degenerate entanglement spectra in a 1/5 magnetization plateau. We also obtain a gapless low-lying continuum in the dynamic spin structure calculated using the dynamical density matrix renormalization group method. We then propose a resonating dimer–monomer liquid state that meets these features.
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- 2020
5. Cluster-based Haldane states in spin-1/2 cluster chains
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Takanori Sugimoto, Katsuhiro Morita, and Takami Tohyama
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Physics ,Condensed Matter - Strongly Correlated Electrons ,Strongly Correlated Electrons (cond-mat.str-el) ,Spins ,Condensed matter physics ,Cluster (physics) ,FOS: Physical sciences ,Condensed Matter::Strongly Correlated Electrons ,State (functional analysis) ,Spin-½ ,Cluster based ,Magnetic field ,Magnetization plateau - Abstract
The Haldane state is a typical quantum and topological state of matter, which exhibits an edge state corresponding to symmetry-protected topological order in a one-dimensional integer spin chain. This edge state can be utilized for a processing unit of quantum computation. Its realization, however, has difficulties with synthesis of integer spin compounds. In contrast, one-half spin systems are more designable due to recent progress on intended synthesis of organic materials, quantum dots, and optical lattices. Here we propose a concept to design the Haldane state with one-half spins by making use of a chain composed of one-half spin clusters. If the clusters contains two spins, the ground state of a chain corresponds to the Affleck--Kennedy--Lieb--Tasaki state. In the case of an odd number of spins in the clusters, we propose a concrete procedure to construct a field-induced Haldane state. We illustrate the procedure with a 5-spin cluster chain., 8 pages, 5 figures
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- 2020
6. Vanishing Wilson ratio as the hallmark of quantum spin-liquid models
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Peter Prelovšek, Jacek Herbrych, Takami Tohyama, and Katsuhiro Morita
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Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Heisenberg model ,FOS: Physical sciences ,Context (language use) ,Square lattice ,Condensed Matter - Strongly Correlated Electrons ,Entropy (classical thermodynamics) ,Condensed Matter::Strongly Correlated Electrons ,Hexagonal lattice ,Singlet state ,Quantum spin liquid ,Wilson ratio ,Mathematical physics - Abstract
We present numerical results for finite-temperature $T>0$ thermodynamic quantities, entropy $s(T)$, uniform susceptibility $\chi_0(T)$ and the Wilson ratio $R(T)$, for several isotropic $S=1/2$ extended Heisenberg models which are prototype models for planar quantum spin liquids. We consider in this context the frustrated $J_1$-$J_2$ model on kagome, triangular, and square lattice, as well as the Heisenberg model on triangular lattice with the ring exchange. Our analysis reveals that typically in the spin-liquid parameter regimes the low-temperature $s(T)$ remains considerable, while $\chi_0(T)$ is reduced consistent mostly with a triplet gap. This leads to vanishing $R(T \to 0)$, being the indication of macroscopic number of singlets lying below triplet excitations. This is in contrast to $J_1$-$J_2$ Heisenberg chain, where $R(T \to 0)$ either remains finite in the gapless regime, or the singlet and triplet gap are equal in the dimerized regime.
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- 2020
7. Magnetic orders induced by RKKY interaction in Tsai-type quasicrystalline approximant Au-Al-Gd
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Takanori Sugimoto, Haruka Miyazaki, Takami Tohyama, and Katsuhiro Morita
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Condensed Matter - Materials Science ,Phase transition ,RKKY interaction ,Materials science ,Strongly Correlated Electrons (cond-mat.str-el) ,Physics and Astronomy (miscellaneous) ,Condensed matter physics ,Magnetic order ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,Quasicrystal ,02 engineering and technology ,Type (model theory) ,021001 nanoscience & nanotechnology ,01 natural sciences ,Crystal ,Condensed Matter - Strongly Correlated Electrons ,0103 physical sciences ,Wavenumber ,General Materials Science ,010306 general physics ,0210 nano-technology ,Fermi Gamma-ray Space Telescope - Abstract
Recent experimental study on Tsai-type quasicrystalline approximant Au-Al-Gd has revealed the presence of magnetic orders and phase transitions with changing the Au/Al concentration. Motivated by the experiment, we theoretically investigate whether a successive change of magnetic orders occurs in a minimal magnetic model including the RKKY interaction only. We find that the model induces multifarious magnetic orders depending on the Fermi wavenumber and gives a good starting point for understanding the experimental observation. In addition, we predict the presence of an undiscovered novel magnetic order called cuboc order at large Fermi wavenumber region., 6 pages, 4 figures
- Published
- 2020
8. Magnetization plateau and supersolid phases in the spin-1/2 antiferromagnetic Heisenberg model on a tetragonally distorted fcc lattice
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Katsuhiro Morita and Takami Tohyama
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Physics ,Condensed Matter::Quantum Gases ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Heisenberg model ,FOS: Physical sciences ,02 engineering and technology ,Cubic crystal system ,021001 nanoscience & nanotechnology ,01 natural sciences ,Supersolid ,Magnetization ,Condensed Matter - Strongly Correlated Electrons ,Lattice (order) ,0103 physical sciences ,Antiferromagnetism ,Hexagonal lattice ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Ground state - Abstract
The Heisenberg model on a face center cubic (fcc) lattice is a typical three-dimensional frustrated spin system expected to have magnetization plateaus and supersolid phases. There are model compounds ${A}_{2}{\mathrm{CoTeO}}_{6}$ ($A=\text{Ca}$, Sr, Pb) for the fcc lattice but with lattice distortions. Motivated by the presence of the compounds, we investigate the ground state of the spin-1/2 antiferromagnetic Heisenberg model on a tetragonally distorted fcc lattice in the magnetic field using a large-size cluster mean-field method for the sake of finding new supersolid phases. We find five supersolid phases in the model, indicating the possibility to observe supersolid phases in these compounds. We also find that one of the supersolid phases is similar to the nonclassical coplanar phase obtained in the $XXZ$ model on the triangular lattice.
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- 2019
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9. Finite-temperature properties of the Kitaev-Heisenberg models on kagome and triangular lattices studied by improved finite-temperature Lanczos methods
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Katsuhiro Morita and Takami Tohyama
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Physics ,Lanczos resampling ,Condensed Matter - Strongly Correlated Electrons ,Condensed matter physics ,Specific heat ,Strongly Correlated Electrons (cond-mat.str-el) ,Statistical Mechanics (cond-mat.stat-mech) ,Lattice (order) ,FOS: Physical sciences ,Condensed Matter::Strongly Correlated Electrons ,Condensed Matter - Statistical Mechanics - Abstract
Frustrated quantum spin systems such as the Heisenberg and Kitaev models on various lattices, have been known to exhibit various exotic properties not only at zero temperature but also for finite temperatures. Inspired by the remarkable development of the quantum frustrated spin systems in recent years, we investigate the finite-temperature properties of the $S=1/2$ Kitaev-Heisenberg models on kagome and triangular lattices by means of finite-temperature Lanczos methods with improved accuracy. In both lattices, multiple peaks are confirmed in the specific heat. To find the origin of the multiple peaks, we calculate the static spin structure factor. The origin of the high-temperature peak of the specific heat is attributed to a crossover from the paramagnetic state to a short-range ordered state whose static spin structure factor has zigzag or linear intensity distributions in momentum space. In the triangular Kitaev model, the "order by disorder" due to quantum fluctuation occurs. On the other hand, in the kagome Kitaev model it does not occur even with both quantum and thermal fluctuations.
- Published
- 2019
- Full Text
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10. Ground state phase diagram of the Kitaev-Heisenberg model on a honeycomb-triangular lattice
- Author
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Katsuhiro Morita, Shigetoshi Sota, Yukihiro Matsubayashi, Masanori Kishimoto, Seiji Yunoki, and Takami Tohyama
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Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Spins ,Condensed matter physics ,Heisenberg model ,High Energy Physics::Lattice ,Monte Carlo method ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,Lattice (order) ,0103 physical sciences ,Hexagonal lattice ,010306 general physics ,0210 nano-technology ,Ground state ,Quantum fluctuation ,Phase diagram - Abstract
The Kitaev-Heisenberg model defined on both honeycomb and triangular lattices has been studied intensively in recent years as a possible model to describe spin-orbital physics in iridium oxides. In the model, there are many phases characteristic for each lattice. However, there is no study of how the phases in the two lattices merge with each other when geometry changes from the honeycomb lattice to triangular lattice. We investigate the ground state of the Kitaev-Heisenberg model defined on the system connecting the honeycomb and triangular lattices, named a honeycomb-triangular lattice. We obtain a ground state phase diagram of this model with classical spins by using the Luttinger-Tisza method and classical Monte Carlo simulation. In addition to known phases in the honeycomb and triangular lattices, we find coexisting phases consisting of the known phases. From the exact diagonalization and density-matrix renormalization-group calculations for the model with quantum spins, we find phases similar to the classical results, implying a small effect of quantum fluctuation on the phase diagram.
- Published
- 2018
11. Ground-state phase diagram of the Kitaev-Heisenberg model on a kagome lattice
- Author
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Masanori Kishimoto, Katsuhiro Morita, and Takami Tohyama
- Subjects
Physics ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Heisenberg model ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,Lattice (order) ,0103 physical sciences ,Quantum system ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Quantum spin liquid ,010306 general physics ,0210 nano-technology ,Ground state ,Quantum fluctuation ,Phase diagram - Abstract
The Kitaev-Heisenberg model on the honeycomb lattice has been studied for the purpose of finding exotic states such as quantum spin liquid and topological orders. On the kagome lattice, in spite of a spin-liquid ground state in the Heisenberg model, the stability of the spin-liquid state has hardly been studied in the presence of the Kitaev interaction. Therefore, we investigate the ground state of the classical and quantum spin systems of the kagome Kitaev-Heisenberg model. In the classical system, we obtain an exact phase diagram that has an eightfold degenerated canted ferromagnetic phase and a subextensive degenerated Kitaev antiferromagnetic phase. In the quantum system, using Lanczos-type exact diagonalization and cluster mean-field methods, we obtain two quantum spin-liquid phases, an eightfold degenerated canted ferromagnetic phase similar to the classical spin system, and an eightfold degenerated, $\mathbf{q}=\mathbf{0},{120}^{\ensuremath{\circ}}$ ordered phase induced by quantum fluctuation. These results may provide a crucial clue to recently observed magnetic structures of the rare-earth-based kagome lattice compounds ${A}_{2}{\mathrm{RE}}_{3}{\mathrm{Sb}}_{3}{\mathrm{O}}_{14}\phantom{\rule{4pt}{0ex}}(A=\text{Mg}$, Zn; $\text{RE}=\text{Pr}$, Nd, Gd, Tb, Dy, Ho, Er, Yb).
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- 2018
12. Magnetization plateaus in the spin-1/2 antiferromagnetic Heisenberg model on a kagome-strip chain
- Author
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Katsuhiro Morita, Shigetoshi Sota, Takami Tohyama, and Takanori Sugimoto
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Physics ,Magnetic structure ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Heisenberg model ,media_common.quotation_subject ,Frustration ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Magnetization ,Condensed Matter - Strongly Correlated Electrons ,Reflection symmetry ,Lattice (order) ,0103 physical sciences ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Spin (physics) ,media_common - Abstract
The spin-$\frac{1}{2}$ Heisenberg model on a kagome lattice is a typical frustrated quantum spin system. The basic structure of a kagome lattice is also present in the kagome-strip lattice in one dimension, where a similar type of frustration is expected. We thus study the magnetization plateaus of the spin-$\frac{1}{2}$ Heisenberg model on a kagome-strip chain with three-independent antiferromagnetic exchange interactions using the density-matrix renormalization-group method. In a certain range of exchange parameters, we find twelve kinds of magnetization plateaus, nine of which have magnetic structures breaking translational and/or reflection symmetry spontaneously. The structures are classified by an array of five-site unit cells with specific bond-spin correlations. In a case with a nontrivial plateau, namely a 3/10 plateau, we find long-period magnetic structure with a period of four unit cells.
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- 2017
13. Field Induced Quantum Phase Transitions in $S=1/2$ $J_1$-$J_2$ Heisenberg Model on the Square Lattice
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Naokazu Shibata and Katsuhiro Morita
- Subjects
Quantum phase transition ,Physics ,Phase transition ,Field (physics) ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Heisenberg model ,Density matrix renormalization group ,General Physics and Astronomy ,FOS: Physical sciences ,01 natural sciences ,Square lattice ,010305 fluids & plasmas ,Condensed Matter - Strongly Correlated Electrons ,0103 physical sciences ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,Spin (physics) ,Ground state - Abstract
We study the magnetic field dependence of the ground state of the S = 1/2 J1–J2 Heisenberg model on the square lattice by the density matrix renormalization group (DMRG) method. With the use of the sine-square deformation, we obtain eight different ground states including plaquette valence-bond crystal with a finite spin gap, transverse Neel, transverse stripe, 1/2 magnetization plateau with up–up–up–down (uuud), and three new states we named the Y-like, V-like, and Ψ states around J2/J1 = 0.55–0.6. The phase transitions from the transverse Neel (at J2/J1 = 0.55) and stripe (at J2/J1 = 0.6) states to the uuud and Y-like states, respectively, are discontinuous, as in the case of a spin flop.
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- 2016
14. Magnetic Phase Diagrams and Magnetization Plateaus of the Spin-1/2 Antiferromagnetic Heisenberg Model on a Square-Kagome Lattice with Three Nonequivalent Exchange Interactions
- Author
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Katsuhiro Morita and Takami Tohyama
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Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Magnetic structure ,Condensed matter physics ,Heisenberg model ,Rotational symmetry ,FOS: Physical sciences ,General Physics and Astronomy ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,Magnetization ,Lattice (order) ,0103 physical sciences ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,010306 general physics ,0210 nano-technology ,Spin (physics) ,Phase diagram - Abstract
Magnetization plateaus in quantum spin systems emerge in two-dimensional frustrated systems such as a kagome lattice. The spin-1/2 antiferromagnetic Heisenberg model on a square-kagome lattice is also appropriate for the study of the magnetization plateau. Motivated by recent experimental findings of such a square kagome lattice with three nonequivalent bonds, we investigate the phase diagrams and magnetization plateaus of the lattice using the exact diagonalization method. In addition to the previously reported 1/3 and 2/3 plateaus in the model with two equivalent bonds, we find a new 2/3 plateau whose magnetic structure is characterized by spontaneously broken four-fold rotational symmetry. The plateau appears only in the case of three nonequivalent bonds. We propose the possibility of finding plateaus including the new one.
- Published
- 2018
15. Exact non-magnetic ground state and residual entropy of S = 1/2 Heisenberg diamond spin lattices
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Naokazu Shibata and Katsuhiro Morita
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Physics ,Condensed Matter - Materials Science ,Condensed matter physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Exchange interaction ,Isotropy ,General Physics and Astronomy ,Diamond ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences ,02 engineering and technology ,engineering.material ,021001 nanoscience & nanotechnology ,01 natural sciences ,Condensed Matter - Strongly Correlated Electrons ,0103 physical sciences ,engineering ,Diamond cubic ,010306 general physics ,0210 nano-technology ,Ground state ,Spin (physics) ,Residual entropy ,Excitation - Abstract
Exactly solvable frustrated quantum spin models consisting of a diamond unit structure are presented. The ground states are characterized by tetramer-dimer states with a macroscopic degeneracy in a certain range of isotropic exchange interaction. The lower bound of the excitation gap is exactly calculated to be finite and the bulk entropy in the limit of zero temperature remains finite depending on the shape of the boundary of system. Residual entropy is in a range of 0~6.1% of the entropy at high temperature for hexagonal diamond lattice and 0~8.4% for square diamond lattice. These diamond lattices are generalized to any dimensions and it is likely to be synthesized experimentally., Comment: 4 pages, 5 figures
- Published
- 2015
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16. New S=1/2 Kagomé antiferromagnets A2Cu 3SnF12: A=Cs and Rb
- Author
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Hidehiro Uekusa, Midori Yano, Kotaro Fujii, Hidekazu Tanaka, Toshio Ono, Katsuhiro Morita, Koichi Kindo, and Yasuo Narumi
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Physics ,History ,Structural phase ,Strongly Correlated Electrons (cond-mat.str-el) ,Hexagonal crystal system ,Exchange interaction ,FOS: Physical sciences ,Magnetic susceptibility ,Computer Science Applications ,Education ,Calculated result ,Crystallography ,Condensed Matter - Strongly Correlated Electrons ,Antiferromagnetism ,Condensed Matter::Strongly Correlated Electrons ,Maxima - Abstract
We synthesized single crystals of the new hexagonal compounds A$_2$Cu$_3$SnF$_{12}$ with A=Cs and Rb, and investigated their magnetic properties. These compounds are composed of Kagom\'{e} layers of corner-sharing CuF$_6$-octahedra. Cs$_2$Cu$_3$SnF$_{12}$ has the proper Kagom\'{e} layer at room temperature, and undergoes structural phase transition at $T_\mathrm{t}\simeq 185$ K. The temperature dependence of the magnetic susceptibility in Cs$_2$Cu$_3$SnF$_{12}$ agrees well with the result of the numerical calculation for $S=1/2$ two-dimensional Heisenberg Kagom\'{e} antiferromagnet down to $T_\mathrm{t}$ with the nearest exchange interaction $J/k_\mathrm{B}\simeq 240$ K. Although the magnetic susceptibility deviates from the calculated result below $T, Comment: 6 pages, 4 figures, to appear in the Proceedings of International Conference on Highly Frustrated Magnetism 2008
- Published
- 2009
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