JOPSS - Search Results

We theoretically investigate the fluctuation of a pure spin current induced by the spin Seebeck effect and spin pumping in a normal metal (NM)/ferromagnet (FM) bilayer system. Starting with a simple FI-NM interface model with both spin-conserving and spin-non-conserving processes, we derive general expressions of the spin current and the spin-current noise at the interface within second-order perturbation of the FI-NM coupling strength, and estimate them for an yttrium iron garnet (YIG) - platinum interface. We show that the spin-current noise can be used to determine the effective spin carried by a magnon modified by the spin-non-conserving process at the interface. In addition, we show that it provides information on the effective spin of a magnon, heating at the interface under spin pumping, and spin Hall angle of the NM.

Journal Articles

Electrical conductivity through a single atomic step measured with the proximity-induced superconducting pair correlation

Kim, H.*; Lin, S.-Z.*; Graf, M.*; Miyata, Yoshinori*; Nagai, Yuki; Kato, Takeo*; Hasegawa, Yukio*

Physical Review Letters, 117(11), p.116802_1 - 116802_5, 2016/09

https://doi.org/10.1103/PhysRevLett.117.116802

Times Cited Count：21 Percentile：75.37(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

Phase competitions and coexistences in quasi-one-dimensional molecular conductors; Exact diagonalization study

Otsuka, Yuichi*; Seo, Hitoshi; Motome, Yukitoshi*; Kato, Takeo*

Physica B; Condensed Matter, 404(3-4), p.479 - 481, 2009/03

https://doi.org/10.1016/j.physb.2008.11.060

Times Cited Count：5 Percentile：25.54(Physics, Condensed Matter)

We investigate ground state properties of a quasi-one-dimensional electron-lattice coupled model for quarter-filled molecular conductors. The effective one-dimensional extended Hubbard model coupled to adiabatic lattice degree of freedom is derived by the inter-chain mean-field approximation and solved by Lanczos exact diagonalization method. We find that the critical behavior among lattice tetramerized states with different charge-lattice ordered patterns is sensitively affected by the inter-chain Coulomb interaction, lattice anharmonicity, and intrinsic dimerization.

Journal Articles

Finite-temperature phase diagram of quasi-one-dimensional molecular conductors; Quantum Monte Carlo study

Otsuka, Yuichi*; Seo, Hitoshi; Motome, Yukitoshi*; Kato, Takeo*

Journal of the Physical Society of Japan, 77(11), p.113705_1 - 113705_4, 2008/11

https://doi.org/10.1143/JPSJ.77.113705

Times Cited Count：30 Percentile：77.48(Physics, Multidisciplinary)

Finite-temperature phase transitions in quasi-one-dimensional quarter-filled systems are investigated using the extended Hubbard model with electron-lattice coupling. By a quantum Monte Carlo method combined with interchain mean-field approximation, we clarify competing and coexisting behaviors among charge ordering, dimer Mott, and spin-Peierls states. The results are compared with experimental data for quasi-one-dimensional molecular conductors such as DCNQI and TMTTF compounds.

Journal Articles

Finite-temperature phase transitions in quasi-one-dimensional molecular conductors

Seo, Hitoshi; Motome, Yukitoshi*; Kato, Takeo*

Journal of the Physical Society of Japan, 76(1), p.013707_1 - 013707_4, 2007/01

https://doi.org/10.1143/JPSJ.76.013707

Times Cited Count：18 Percentile：66.94(Physics, Multidisciplinary)

Phase transitions in 1/4-filled quasi-one-dimensional molecular conductors are studied theoretically on the basis of extended Hubbard chains including electron-lattice interactions coupled by interchain Coulomb repulsion. We apply the numerical quantum transfer-matrix method to an effective one-dimensional model, treating the interchain term within mean-field approximation. Finite-temperature properties are investigated for the charge ordering, the "dimer Mott" transition (bond dimerization), and the spin-Peierls transition (bond tetramerization). A coexistent state of charge order and bond dimerization exhibiting dielectricity is predicted in a certain parameter range, even when intrinsic dimerization is absent.

Oral presentation

Phase competitions and phase coexistences in quasi-one-dimensional molecular conductors

Seo, Hitoshi; Kato, Takeo*; Motome, Yukitoshi*

no journal, ,

We have theoretically investigated finite-temperature properties ofIn this work, we aim at providing a unified view for such compounds by studying a quasi-one-dimensional model numerically, whose Hamiltonian iswritten as ${cal H}_{rm 1D} + {cal H}_{perp} + {cal H}_{rm e-l}$ . The first term ${cal H}_{rm 1D}$ is the one-dimensional extended Hubbard model in the chain direction, the second term ${cal H}_{perp}$ denotes the interchain interactions such as the Coulomb repulsion and the exchange coupling, and the third term ${cal H}_{rm e-l}$ represents the electron-lattice interaction. We use two methods to treat this model. One is the transfer matrix method applied to the effective one-dimensional model by treating ${cal H}_{perp}$ within the "interchain mean-field" approximation. Another is the quantum Monte Carlo simulation with stochastic series expansionwhere the interchain interactionsas well as thermal fluctuations of lattice distortions can be taken into account in an unbiased way. We will compare the numerical results with the experimental dataso as to elucidate the origin of the various properties seen in the actual compounds.

Oral presentation

Coexistences and competitions of symmetry broken states in quasi-one-dimensional molecular conductors; A Finite-temperature study

Seo, Hitoshi; Kato, Takeo*; Motome, Yukitoshi*

no journal, ,

We have theoretically investigated finite-temperature properties of quarter-filled molecular conductors with quasi-one-dimensional structures. They exhibit a large variety of electronic and electron-lattice coupled phases, and since the systems have similar noninteracting electronic structures, such a variety in their physical properties implies the importance of strong correlation effects. In this work, we aim at providing a unified view for these compounds by studying a electron-lattice coupled quasi-one-dimensional model. We apply two numerical methods to this model, by treating the lattice degree of freedom as classical variables. One is the quantum transfer matrix method applied to an effective one-dimensional model. Another is the quantum Monte Carlo simulation with stochastic series expansion where the interchain interaction as well as the thermal fluctuation of the lattice can be taken into account in an unbiased way. We will compare numerical results with experimental data at a quantitative level so as to elucidate the origin of the various properties seen in the actual compounds.

Oral presentation

Numerical study on phase competitions and phase coexistences in quasi-one-dimensional molecular conductors

Seo, Hitoshi; Kato, Takeo*; Motome, Yukitoshi*

no journal, ,

no abstracts in English

Oral presentation

Numerical study on electron-lattice coupled properties of quasi-one-dimensional molecular conductors

Seo, Hitoshi; Kato, Takeo*; Motome, Yukitoshi*

no journal, ,

no abstracts in English