Shu Tanaka

Applicability of scaling behavior and power laws in the analysis of the magnetocaloric effect in second-order phase transition materials

This work was supported by JSPS KAKENHI Grants No. 25420698 (R.T. and S.T.), No. 15K17720 (S.T.), No. 15H03699 (S.T.), and by the Spanish MINECO and EUFEDER (Project MAT2013-45165-P) and the PAI of the Regional Government of Andalucia (V.F.). S.T. was also supported by Waseda University Grant for Special Research Projects (Project No. 2015B-514) and C.R.-M. is grateful to FPI-UAM graduate scholarship program and Fundacion Universia for financial support

Successive phase transitions and phase diagrams for the quasi-two-dimensional easy-axis triangular antiferromagnet Rb4Mn(MoO4)3

Using magnetic, thermal and neutron measurements we show that Rb4Mn(MoO4)3 is a quasi-2D triangular Heisenberg antiferromagnet with easy-axis anisotropy and successive transitions bracketing an intermediate collinear phase. An accurate quantitative account of the phase diagram is achieved through Monte Carlo simulation of a spin Hamiltonian with easy-axis anisotropy D=0.22J.

Entanglement in valence-bond-solid states on symmetric graphs

We study quantum entanglement in the ground state of the Affleck–Kennedy–Lieb–Tasaki model defined on two-dimensional graphs with reflection and/or inversion symmetry. The ground state of this spin model is known as the valence-bond-solid state. We investigate the properties of a reduced density matrix of a subsystem which is a mirror image of the other one. Thanks to reflection symmetry, the eigenvalues of the reduced density matrix can be obtained by numerically diagonalizing a real symmetric matrix whose elements are calculated by Monte Carlo integration. We calculate the von Neumann entropy of the reduced density matrix. The obtained results indicate that there is some deviation from the naive expectation that the von Neumann entropy per valence bond on the boundary between the subsystems is ln 2. This deviation is interpreted in terms of the hidden spin chain along the boundary between the subsystems. In some cases where graphs are on ladders, the numerical results are analytically or algebraically confirmed.

Dynamical properties of potts model with invisible states

We study dynamic behavior of Potts model with invisible states near the first-order phase transition temperature. This model is regarded as a standard model to analyse nature of phase transition. We can control the energy barrier between the ordered state and disordered state without changing the symmetry which breaks at the transition point. We focus on melting process starting from the perfect ordered state. We calculate time-dependency of the order parameter, density of invisible state, and internal energy. All of them show two-step relaxation behavior. We also analyze the relationship between the characteristic melting time and characteristic scale of the energy barrier by changing the number of invisible states. We find that characteristic melting time increases as the energy barrier enlarges in this model. This model is regarded as a fundamental model to analyze dynamic behavior near the first-order phase transition point.

Entanglement spectra of the two-dimensional Affleck-Kennedy-Lieb-Tasaki model: Correspondence between the valence-bond-solid state and conformal field theory

We investigate the entanglement properties of the valence-bond-solid (VBS) state defined on twodimensional lattices, which is the exact ground state of the Affleck-Kennedy-Lieb-Tasaki model. It is shown that the entanglement entropy obeys an area law and the non-universal prefactor of the leading term is strictly less than ln 2. The analysis of entanglement spectra for various lattices reveals that the reduced density matrix associated with the VBS state is closely related to a thermal density matrix of a holographic spin chain, whose spectrum is reminiscent of that of the spin-1/2 Heisenberg chain. This correspondence is further supported by comparing the entanglement entropy in the holographic spin chain with conformal field theory predictions.

Phase transition in potts model with invisible states

We study phase transition in the ferromagnetic Potts model with invisible states that are added as redundant states by mean-field calculation and Monte Carlo simulation. Invisible states affect the entropy and the free energy, although they do not contribute to the internal energy. The internal energy and the number of degenerated ground states do not change, if invisible states are introduced into the standard Potts model. A second-order phase transition takes place at finite temperature in the standard

Magnetic properties of thin Cr layers in multilayer systems studied through 119Sn Mössbauer probes

q

Magnetic ordered structure dependence of magnetic refrigeration efficiency

-state ferromagnetic Potts model on two-dimensional lattice for

Entanglement spectra of the quantum hard-square model: Holographic minimal models

q=2,3

Estimation of Spin-Spin Interaction by Weak Measurement Scheme

, and 4. However, our present model on two-dimensional lattice undergoes a first-order phase transition with spontaneous