arXiv subjects

Jun Sato

Publications and source records attributed to Jun Sato.

At least 37 records · Page 2Linked to original sources

arXiv2013

Finite-size scaling behavior of Bose-Einstein condensation in the 1D Bose gas

Through exact numerical solutions we show Bose-Einstein condensation (BEC) for the one-dimensional (1D) bosons with repulsive short-range interactions at zero temperature by taking a particular large size limit. Following the Penrose-Onsager criterion of BEC, we define condensate fraction by the fraction of the largest eigenvalue of the one-particle reduced density matrix. % We show the finite-size scaling behavior such that condensate fraction is given by a scaling function of one-variable: interaction parameter multiplied by a power of particle number. Condensate fraction is nonzero and constant for any large value of particle number or system size, if the interaction parameter is proportional to the negative power of particle number. %Here the interaction parameter is defined by the coupling constant of the delta-function potentials devided by the density. %With the scaling behavior we derive various themodynamic limits where condensate fraction is constant for any large system size; for instance, it is the case even in the system of a finite particle number.

cond-mat.quant-gas↗

arXiv2013

Penetration of a magnetic wall into thin ferromagnetic electrodes of a nano-contact spin valve

We theoretically analyzed a magnetic wall confined in a nano-contact spin valve paying special attention to the penetration of the magnetic wall into thin ferromagnetic electrodes. We showed that, compared with the Bloch wall, the penetration of the Neel wall is suppressed by increases of the demagnetization energy. We found the optimal conditions of the radius and height of the nano-contact to maximize the power of the current-induced oscillation of the magnetic wall. We also found that the thermal stability of the Bloch wall increases when the nano-contact's radius increases or height decreases.

cond-mat.mes-hall↗

arXiv2012

Long time asymptotics of the totally asymmetric simple exclusion process

We study the long time asymptotics of the relaxation dynamics of the totally asymmetric simple exclusion process on a ring. Evaluating the asymptotic amplitudes of the local currents by the algebraic Bethe ansatz method, we find the relaxation times starting from the step and alternating initial conditions are governed by different eigenvalues of the Markov matrix. In both cases, the scaling exponents of the leading asymptotic amplitudes with respect to the total number of sites are found to be -1. We also study the asymptotics of correlation functions such as the emptiness formation probability.

cond-mat.stat-mech↗

arXiv2012

Quantum dark solitons in the 1D Bose gas and the superfluid velocity

We give explicit connections of quantum one-hole excited states to classical solitons for the one-dimensional Bose gas with repulsive short-range interactions. We call the quantum states connected to classical solitons the quantum soliton states. We show that the matrix element of the canonical field operator between quantum soliton states with $N-1$ and $N$ particles is given by a dark soliton of the Gross-Pitaevskii equation in the weak coupling case. We suggest that the matrix element corresponds to the order parameter of BEC in the quantum soliton state. The result should be useful in the study of many-body effects in Bose-Einstein condensation and superfluids. For instance, we derive the superfluid velocity for a quantum soliton state.

cond-mat.quant-gas↗

arXiv2012

Exact relaxation dynamics of a localized many-body state in the 1D bose gas

Through an exact method we numerically solve the time evolution of the density profile for an initially localized state in the one-dimensional bosons with repulsive short-range interactions. We show that a localized state with a density notch is constructed by superposing one-hole excitations. The initial density profile overlaps the plot of the squared amplitude of a dark soliton in the weak coupling regime. We observe the localized state collapsing into a flat profile in equilibrium for a large number of particles such as N=1000. The relaxation time increases as the coupling constant decreases, which suggests the existence of off-diagonal long-range order. We show a recurrence phenomenon for a small number of particles such as N=20.

cond-mat.quant-gas↗

arXiv2012

Exact Relaxation Dynamics in the Totally Asymmetric Simple Exclusion Process

The relaxation dynamics of the one-dimensional totally asymmetric simple exclusion process on a ring is considered in the case of step initial condition. Analyzing the time evolution of the local particle densities and currents by the Bethe ansatz method, we examine their full relaxation dynamics. As a result, we observe peculiar behaviors, such as the emergence of a ripple in the density profile and the existence of the excessive particle currents. Moreover, by making a finite-size scaling analysis of the asymptotic amplitudes of the local densities and currents, we find the scaling exponents with respect to the total number of sites to be -3/2 and -1 respectively.

cond-mat.stat-mech↗

arXiv2011

Quantum Group U_q(sl(2)) Symmetry and Explicit Evaluation of the One-Point Functions of the Integrable Spin-1 XXZ Chain

We show some symmetry relations among the correlation functions of the integrable higher-spin XXX and XXZ spin chains, where we explicitly evaluate the multiple integrals representing the one-point functions in the spin-1 case. We review the multiple-integral representations of correlation functions for the integrable higher-spin XXZ chains derived in a region of the massless regime including the anti-ferromagnetic point. Here we make use of the gauge transformations between the symmetric and asymmetric R-matrices, which correspond to the principal and homogeneous gradings, respectively, and we send the inhomogeneous parameters to the set of complete 2s-strings. We also give a numerical support for the analytical expression of the one-point functions in the spin-1 case.

cond-mat.stat-mech↗

arXiv2010

Exact Yrast Spectra of Cold Atoms on a Ring

We propose a methodology to construct excited states with a fixed angular momentum, namely, "yrast excited states" of finite-size one-dimensional bosonic systems with periodic boundary conditions. The excitation energies such as the first yrast excited energy are calculated through the system-size asymptotic expansion and expressed analytically by dressed energy. Interestingly, they are grouped into sets of almost degenerate energy levels. The low-lying excitation spectrum near the yrast state is consistent with the $ U(1)$ conformal field theories if the total angular momentum is given by an integral multiple of particle number; i.e., if the system is supercurrent.

cond-mat.quant-gas↗

arXiv2010

Spectral Properties of Interacting One-Dimensional Spinless Fermions

The spectral properties of the spinless fermion model with nearest-neighbor repulsive interactions on a one-dimensional lattice are investigated using the Bethe ansatz. Although its bulk quantities are exactly the same as those of the spin-1/2 XXZ chain, the difference in the statistics of particles causes substantial effects on spectral features, such as gapless points of dispersion relations and line shapes of spectral functions. In this Letter, we clarify the origin of the differences in spectral features between fermionic and bosonic systems in terms of Bethe ansatz solutions. We also confirm that the two-string solutions have considerable spectral weights in the high-energy regime.

cond-mat.str-el↗

arXiv2009

Microscopic Structural Relaxation in a Sheared Supercooled Colloidal Liquid

The rheology of dense amorphous materials under large shear strain is not fully understood, partly due to the difficulty of directly viewing the microscopic details of such materials. We use a colloidal suspension to simulate amorphous materials, and study the shear-induced structural relaxation with fast confocal microscopy. We quantify the plastic rearrangements of the particles in several ways. Each of these measures of plasticity reveals spatially heterogeneous dynamics, with localized regions where many particles are strongly rearranging by these measures. We examine the shapes of these regions and find them to be essentially isotropic, with no alignment in any particular direction. Furthermore, individual particles are equally likely to move in any direction, other than the overall bias imposed by the strain.

cond-mat.soft↗

arXiv2009

Dipolar field effect on microwave oscillation in a domain wall spin-valve

We examined dipolar field effects on the microwave generation in the domain wall spin-valve by solving simultaneously the Landau-Lifshitz-Gilbert and Zhang-Levy-Fert diffusion equations. By numerically analyzing dipolar field dependence, we showed that the microwave generation needs the dipole-dipole interaction for a 180$^\circ$ domain wall and the amplitude of the microwave voltage signal depends strongly on the exchange length. In order to design a microwave generator using the domain wall spin-valve with high efficiency, we propose that the materials with short exchange length are preferred.

cond-mat.mes-hall↗

arXiv2009

Theory of spin accumulation and spin transfer torque in a magnetic domain wall

We study spin accumulation and spin transfer torque in a domain wall by solving the Boltzmann equation with a diffusion approximation. We obtained the analytical expressions of spin accumulation and spin transfer torque. Both the adiabatic and the non-adiabatic components of the spin transfer torque oscillate with the thickness of the domain wall. We show that the oscillation plays a dominant role in the non-adiabatic torque when the domain wall thickness is less than the spin-flip length, which is defined by the product of the Fermi velocity and the spin-flip scattering time.

cond-mat.mes-hall↗

arXiv2009

Current-induced microwave excitation of a domain wall confined in a magnetic wire with bi-axial anisotropy

We studied the current-induced magnetization dynamics of a domain wall confined in a magnetic wire with bi-axial anisotropy. We showed that above the threshold current density, breathing-mode excitation, where the thickness of the domain wall oscillates, is induced by spin-transfer torque. We found that the breathing-mode can be applied as a source of microwave oscillation because the resistance of the domain wall is a function of the domain wall thickness. In a current sweep simulation, the frequency of the breathing-mode exhibits hysteresis because of the confinement.

cond-mat.mes-hall↗

arXiv2009

Simulation of current-induced microwave oscillation in geometrically confined domain wall

We studied magnetization dynamics of a geometrically confined domain wall under dc current by solving simultaneously the Landau-Lifshitz-Gilbert equation and diffusion equation for spin accumulation. We showed that the oscillation motion of the domain wall is driven by the spin-transfer torque and the dc current is converted to the ac voltage signal. The results means that the geometrically confined domain wall is applicable as a source of microwave oscillator.

cond-mat.mes-hall↗

arXiv2009

Current-perpendicular-to-plane magnetoresistance of a domain wall confined in a nano-oxide-layer

We theoretically study the current-perpendicular-to-plane magnetoresistance of a domain wall confined in a current-confined-path (CCP) structure made of a nano-oxide-layer (NOL). In order to calculate the MR ratio of the system, the continuity equations for charge and spin currents are numerically solved with the three-dimensional CCP geometry by use of finite element method. It is confirmed that the MR ratio is enhanced by the CCP structure, which is consistent with the experimental results.

cond-mat.mes-hall↗

arXiv2009

Magnetic structure of domain walls confined in a nano-oxide layer

In the recent years, a spin-valve was developed with a current-confined-path structure consisting of a non-oxide-layer (NOL). We analyze magnetic structures of the current-confinedpath in the nano-oxide layer sandwiched between ferromagnetic electrodes and clarify the dependency of the magnetic structure on the shape and size of the current-confined-path. Our results of stiffness energy density and thermal stability shows that we should fabricate a CPP spin-valve with narrow current-confinedpaths with large aspect ratio and strong constriction in order to enhance the MR ratio.

cond-mat.mes-hall↗

arXiv2008

Effective Resistance Mismatch and Magnetoresistance of a CPP-GMR system with Current-Confined-Paths

We theoretically study the magnetoresistance of a CPP-GMR system with current confined paths (CCP) in the framework of Valet-Fert theory. The continuity equations for charge and spin currents are numerically solved with the three-dimensional CCP geometry by use of finite element method. It is confirmed that the MR ratio is enhanced by the CCP structure, which is consistent with the experimental results. Moreover, we find that there exists a certain contact width which maximize the MR ratio. We show that the contact width which maximize the MR ratio is well described by the effective resistance matching.

cond-mat.mes-hall↗

arXiv2007

Density matrix elements and entanglement entropy for the spin-1/2 XXZ chain at $Δ$=1/2

We have analytically obtained all the density matrix elements up to six lattice sites for the spin-1/2 Heisenberg XXZ chain at $Δ=1/2$. We use the multiple integral formula of the correlation function for the massless XXZ chain derived by Jimbo and Miwa. As for the spin-spin correlation functions, we have newly obtained the fourth- and fifth-neighbour transverse correlation functions. We have calculated all the eigenvalues of the density matrix and analyze the eigenvalue-distribution. Using these results the exact values of the entanglement entropy for the reduced density matrix up six lattice sites have been obtained. We observe that our exact results agree quite well with the asymptotic formula predicted by the conformal field theory.

cond-mat.stat-mech↗