arXiv subjects

Kazue Kudo

Publications and source records attributed to Kazue Kudo.

40 records · Page 3Linked to original sources

arXiv2005

Energy diffusion in frustrated quantum spin chains exhibiting Gaussian orthogonal ensemble level statistics

Frustrated quantum $XXZ$ spin chains with the next-nearest-neighbor (NNN) couplings are typically deterministic many-body systems exhibiting Gaussian orthogonal ensemble (GOE) spectral statistics. We investigate energy diffusion for these spin chains in the presence of a periodically oscillating magnetic field. Diffusion coefficients are found to obey the power law with respect to both the field strength and driving frequency with its power varying depending on the linear response and non-perturbative regimes. The widths of the linear response and the non-perturbative regimes depend on the strength of frustrations. We have also elucidated a mechanism for oscillation of energy diffusion in the case of weakened frustrations.

cond-mat.stat-mech↗

arXiv2004

Level statistics of XXZ spin chains with a random magnetic field

The level-spacing distribution of a spin 1/2 XXZ chain is numerically studied under random magnetic field. We show explicitly how the level statistics depends on the lattice size L, the anisotropy parameter $Δ$, and the mean amplitude of the random magnetic field h. In the energy spectrum, quantum integrability competes with nonintegrability derived from the randomness, where the XXZ interaction is modified by the parameter $Δ$. When $Δ\ne 0$, the level-spacing distribution mostly shows Wigner-like behavior, while when $Δ$=0, Poisson-like behavior appears although the system is nonintegrable due to randomness. Poisson-like behavior also appears for $Δ\ne 0$ in the large h limit. Furthermore, the level-spacing distribution depends on the lattice size L, particularly when the random field is weak.

cond-mat.stat-mech↗

arXiv2003

Unexpected non-Wigner behavior in level-spacing distributions of next-nearest-neighbor coupled XXZ spin chains

The level-spacing distributions of XXZ spin chains with next-nearest-neighbor couplings are studied under periodic boundary conditions. We confirm that integrable XXZ spin chains mostly have the Poisson distribution as expected. On the contrary, the level-spacing distributions of next-nearest-neighbor coupled XXZ chains are given by non-Wigner distributions. It is against the expectations, since the models are nonintegrable.

cond-mat.stat-mech↗

arXiv2003

On the Magnetic-Field Dependence of the Longitudinal Ultrasonic Attenuation in a Type-II Superconductor

We propose a simple method by which we can explain the magnetic-field dependence of the longitudinal ultrasonic attenuation in a type-II superconductor. It gives a curve which is in good agreement with experimental data, in paticular, near the lower critical field H_c1. We compare it with conventional methods, which is not in good agreement with the experimental data near H_c1 but near the upper critical field H_c2.

cond-mat.supr-con↗