arXiv subjects

Yukiyasu Ozeki

Publications and source records attributed to Yukiyasu Ozeki.

10 recordsLinked to original sources

arXiv2026

Dynamical scaling study for the estimation of dynamical exponent $z$ of three-dimensional XY spin glass model

To analyze the $\pm J$ XY spin-glass in three dimensions, we verified a method aimed at obtaining a high-precision dynamical exponent $z$ from the correlation length in the nonequilibrium relaxation process. The obtained $z$ yielded consistent and highly accurate results in previous studies for relatively well-studied models---specifically, the three-dimensional (3D) ferromagnetic Ising model and the 3D $\pm J$ Ising model. Building on these previous studies, we used this method and the dynamical scaling method to analyze the 3D $\pm J$ XY model and obtained highly precise critical temperatures and exponents. The estimated transition temperatures satisfy $T_{\mathrm{SG}}<T_{\mathrm{CG}}$ and are consistent with the spin chirality decoupling picture.

cond-mat.stat-mech↗

arXiv2026

Critical Universality of the SU (2) Gauge Glass Model Analyzed by the Dynamical Scaling Method

We investigate the critical phenomena of the three-dimensional (3D) $SU(2)$ gauge glass model, which can be regarded as the $O(4)$ spin-glass model with gauge symmetry. Using Monte Carlo simulations and the non-equilibrium relaxation method, we examine the critical behavior along phase boundaries across various degrees of disorder. Consistent with previous studies, we verify that weak disorder is irrelevant to the universality class; the critical behavior of the ferromagnetic-paramagnetic transition remains in the 3D $O(4)$ universality class of the pure ferromagnetic system. Additionally, we demonstrate that the paramagnetic-spin glass transition exhibits universal critical behavior independent of the disorder. Our findings provide valuable insights into the fundamental properties and universality of gauge glass models.

cond-mat.dis-nn↗

arXiv2026

Dynamical scaling method improved by a deep learning approach

We propose a dynamical scaling analysis improved by a deep learning approach. While Gaussian process regression has been widely employed for estimating scaling parameters, its computational cost for parameter optimization becomes a limitation in dynamical scaling analysis, where large datasets are involved. In contrast, the present method employs a neural network, which significantly reduces the computational cost and enables the use of the entire dataset that was inaccessible with Gaussian process regression. We applied the method to the 2D Ising model and the 2D 3-state Potts model, achieving higher accuracy and computational efficiency than conventional approaches.

cond-mat.stat-mech↗

arXiv2024

Improvement of analysis for relaxation of fluctuations by the use of Gaussian process regression and extrapolation method

The nonequilibrium relaxation (NER) method, which has been used to investigate equilibrium systems via their nonequilibrium behavior, has been widely applied to various models to estimate critical temperatures and critical exponents. Although the estimation of critical temperatures has become more reliable and reproducible, that of critical exponents raises concerns about the method's reliability. Therefore, we propose a more reliable and reproducible approach using Gaussian process regression. In addition, the present approach introduces statistical errors through the bootstrap method by combining them using the extrapolation method. Our estimation for the two-dimensional Ising model yielded $β= 0.12504(6)$, $γ= 1.7505(10)$, and $ν= 1.0003(6)$, consistent with the exact values. The value $z = 2.1669(9)$ is reliable because of the high accuracy of these exponents. We also obtained the critical exponents for the three-dimensional Ising model and found that they are close to those reported in a previous study. Thus, for systems undergoing second-order transitions, our approach improves the accuracy, reliability, and reproducibility of the NER analysis. Because the proposed approach requires the relaxation of some observables from Monte Carlo simulations, its simplicity imparts it with significant potential.

cond-mat.stat-mech↗

arXiv2005

Gauge Theory for Quantum Spin Glasses

The gauge theory for random spin systems is extended to quantum spin glasses to derive a number of exact and/or rigorous results. The transverse Ising model and the quantum gauge glass are shown to be gauge invariant. For these models, an identity is proved that the expectation value of the gauge invariant operator in the ferromagnetic limit is equal to the one in the classical equilibrium state on the Nishimori line. As a result, a set of inequalities for the correlation function are proved, which restrict the location of the ordered phase. It is also proved that there is no long-range order in the two-dimensional quantum gauge glass in the ground state. The phase diagram for the quantum XY Mattis model is determined.

cond-mat.dis-nn↗

arXiv2003

Dynamical Gauge Theory for the XY Gauge Glass Model

Dynamical systems of the gauge glass are investigated by the method of the gauge transformation.Both stochastic and deterministic dynamics are treated. Several exact relations are derived among dynamical quantities such as equilibrium and nonequilibrium auto-correlation functions, relaxation functions of order parameter and internal energy. They provide physical properties in terms of dynamics in the SG phase, a possible mixed phase and the Griffiths phase, the multicritical dynamics and the aging phenomenon. We also have a plausible argument for the absence of re-entrant transition in two or higher dimensions.

cond-mat.dis-nn↗

arXiv2002

Energy fluctuations at the multicritical point in two-dimensional spin glasses

We study the two-dimensional +/-J Ising model, three-state Potts model and four-state Potts model, by the numerical transfer matrix method to investigate the behaviour of the sample-to-sample fluctuations of the internal energy on the Nishimori line. The result shows a maximum at the multicritical point in all the models we investigated. The large sample-to-sample fluctuations of the internal energy as well as the existence of a singularity in these fluctuations imply that the bond configuration (or, equivalently, the distribution of frustrated plaquettes) may be experiencing a non-trivial change of its behaviour at the multicritical point. This observation is consistent with the picture that the phase transition at the multicritical point is of geometry-induced nature.

cond-mat.dis-nn↗

arXiv1996

Aging Relation for Ising Spin Glasses

We derive a rigorous dynamical relation on aging phenomena -- the aging relation -- for Ising spin glasses using the method of gauge transformation. The waiting-time dependence of the auto-correlation function in the zero-field-cooling process is equivalent with that in the field-quenching process. There is no aging on the Nishimori line; this reveals arguments for dynamical properties of the Griffiths phase and the mixed phase. The present method can be applied to other gauge-symmetric models such as the XY gauge glass.

cond-mat.dis-nn↗

arXiv1995

Ground-State Phase Diagrams of the Two-Dimensional Quantum Heisenberg Spin Glass Models

Ground-state properties of the two-dimensional $S=1/2$ random Heisenberg models are investigated by the exact-diagonalization method. The phase diagram of the bond-random model (the $\pm J$ model) is the same as that of the corresponding Ising spin glass model, in spite of quantum fluctuation. In the site-random model, the spin glass phase exists at least in the ferro-rich case. In comparison with the corresponding Ising model, the Néel phase of this model becomes much narrower in the ferro-rich case, while it is comparable in the antiferro-rich case. KEYWORDS: quantum spin glass, Heisenberg model, ground-state phase transition, site-random model, exact diagonalization

cond-mat↗

arXiv1995

Long-Range Order of the Site-Random Spin Glass Model

The site-random Ising spin glass model is investigated. We find a rigorous symmetry for the SG correlation and the free energy, which provides some restrictions in the phase diagram. Using the defect energies calculated by the numerical transfer matrix method, we obtain evidence for the existence of the SG phase in the two-dimensional Ising system. We suggest that the transitions from the FM and the AF phases in the ground state in this model can be explained by the percolated-cluster picture, which is quite different from the frustration picture in the conventional $\pm J$ model.

cond-mat↗