arXiv subjects

Atsuo Shitade

Publications and source records attributed to Atsuo Shitade.

24 records · Page 2Linked to original sources

arXiv2014

Bulk angular momentum and Hall viscosity in chiral superconductors

We establish the Berry-phase formulas for the angular momentum (AM) and the Hall viscosity (HV) to investigate chiral superconductors (SCs) in two and three dimensions. The AM is defined by the temporal integral of the anti-symmetric momentum current induced by an adiabatic deformation, while the HV is defined by the symmetric momentum current induced by the symmetric torsional electric field. Without suffering from the system size or geometry, we obtain the macroscopic AM $L_z = \hbar m N_0/2$ at zero temperature in full-gap chiral SCs, where $m$ is the magnetic quantum number and $N_0$ is the total number of electrons. We also find that the HV is equal to half the AM at zero temperature not only in full-gap chiral SCs as is well-known but also in nodal ones, but its behavior at finite temperature is different in the two cases.

cond-mat.supr-con↗

arXiv2014

Theory of Charge and Heat Polarizations with the Keldysh Formalism

We investigate the heat polarization, a heat analog of the charge polarization, by using the gauge-covariant Keldysh formalism. In contrast to the charge-heat analogy naively expected, we find that the heat polarization does not appear spontaneously, since it consists not only of the heat-transfer contribution but of the heat-generation contribution, leading to the Mott rule. Nonetheless, it can be induced by a torsional magnetic field in $(3+1)$-D topological insulators and superconductors, which is described by the temporal part of the Nieh-Yan action.

cond-mat.mes-hall↗

arXiv2013

Quantum Theory of Heat Magnetization

We give the thermodynamic definition of the heat magnetization, and calculate with use of the Keldysh formalism in a curved spacetime. The heat magnetization is conjugate to a torsional magnetic field, which is analogous to the fact that the orbital magnetization is conjugate to a magnetic field. The formula is valid in insulators and metals at finite temperature even in disordered or interacting systems.

cond-mat.mes-hall↗

arXiv2012

Anomalous Hall Effect in Ferromagnetic Metals: Role of Phonons at Finite Temperature

The anomalous Hall effect in a multiband tight-binding model is numerically studied taking into account both elastic scattering by disorder and inelastic scattering by the electron-phonon interaction. The Hall conductivity is obtained as a function of temperature $T$, inelastic scattering rate $γ$, chemical potential $μ$, and impurity concentration $x_{\rm imp}$. We find that the new scaling law holds over a wide range of these parameters; $-σ_{xy}= (ασ_{xx0}^{-1} + βσ_{xx0}^{-2}) σ_{xx}^2 + b$, with $σ_{μν}$ ($σ_{μν0}$) being the conductivity tensor (with only elastic scattering), which corresponds to the recent experimental observation [Phys. Rev. Lett. {\bf 103} (2009) 087206]. The condition of this scaling is examined. Also, it is found that the intrinsic mechanism depends on temperature under a resonance condition.

cond-mat.str-el↗

arXiv2010

Manipulation of two spin qubits in a double quantum dot using an electric field

We propose purely electric manipulation of spin qubits by means of the spin-orbit interaction (SOI) {\it without magnetic field or magnets} in a double-quantum dot. All the unitary transformations can be constructed by the time-dependent Dzyaloshinsky-Moriya interaction between the two spins, which arises from the Rashba SOI modulated by electric field. As a few demonstrations, we study both analytically and numerically the three operations, i.e., (A) the spin initialization, (B) the two-spin rotation in the opposite directions, and (C) the two-spin rotation in the same direction. The effects of the relaxation and the feasibility of this proposal are also discussed.

cond-mat.mes-hall↗

arXiv2009

Quantum spin Hall effect in a transition metal oxide Na2IrO3

We study theoretically the electronic states in a $5d$ transition metal oxide Na$_2$IrO$_3$, in which both the spin-orbit interaction and the electron correlation play crucial roles. Tight-binding model analysis together with the fisrt-principles band structure calculation predicts that this material is a layered quantum spin Hall system. Due to the electron correlation, an antiferromagnetic order first develops at the edge, and later inside the bulk at low temperatures.

cond-mat.str-el↗