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Hajime Yoshino

Publications and source records attributed to Hajime Yoshino.

63 records · Page 4Linked to original sources
arXiv2000

Numerical Study on Aging Dynamics in Ising Spin-Glass Models: Temperature-Change Protocols

By means of Monte Carlo simulations on the three-dimensional Ising spin-glass model, we have studied aging phenomena with various temperature($T$)-change protocols. Particularly, a $T$-shift protocol, in which a system is first quenched to and aged for a period $t_{\rm w1}$ at a temperature $T_1$, and subsequently aged at a new temperature $T_2$ is closely investigated. Most importantly, the mean size of domains, which is extracted from the replica-overlap function, was found to grow monotonically without any appreciable decrease by the $T$-change. We also found the relaxation of energy density and spin auto-correlation function during the $T$-shift process can be explained within the following picture: the dynamics finally crossovers to an isothermal aging of $T_2$ at around $t_2 \simeq t_{\rm w1}^{\rm (eff)}$ after the $T$-change, where $t_{\rm w1}^{\rm (eff)}$ is an effective waiting time related with $t_{\rm w1}$, but in the transient regime $t_2 \lt t_{\rm w1}^{\rm (eff)}$, adjustment of the population of thermally active droplets from that at $T_1$ to $T_2$ takes place very slowly. Implications of the results on aging phenomena in other $T$-change protocols such as $T$-cycling and continuous $T$-change with an intermittent stop observed by simulations as well as experiments are discussed.

cond-mat.dis-nn↗
arXiv2000

Numerical Study on Aging Dynamics in the 3D Ising Spin-Glass Model. II. Quasi-Equilibrium Regime of Spin Auto-Correlation Function

Using Monte Carlo simulations, we have studied isothermal aging of three-dimensional Ising spin-glass model focusing on quasi-equilibrium behavior of the spin auto-correlation function. Weak violation of the time translational invariance in the quasi-equilibrium regime is analyzed in terms of {\it effective stiffness} for droplet excitations in the presence of domain walls. Within the range of computational time window, we have confirmed that the effective stiffness follows the expected scaling behavior with respect to the characteristic length scales associated with droplet excitations and domain walls, whose growth law has been extracted from our simulated data. Implication of the results are discussed in relation to experimental works on ac susceptibilities.

cond-mat.dis-nn↗
arXiv1999

Numerical Study of Aging Phenomena in Short-Ranged Spin Glasses

Aging phenomena of short-range Ising spin glass models have been investigated using Monte Carlo simulations. It is found that in the low-temperature spin-glass phase the mean domain size exhibits a crossover from a power-law growth associated with the critical fluctuation at the transition temperature to slower growth inherent in the low-temperature phase. The temperature dependence of the growth law of the domain size can be almost explained by this crossover. We also find that the spin-autocorrelation function in the quasi-equilibrium regime follows the expected scaling behavior from the droplet theory expressed in terms of the mean domain size and a characteristic length scale of droplet excitations.

cond-mat.dis-nn↗
arXiv1999

Numerical Study on Aging Dynamics in the 3D Ising Spin-Glass Model. I. Energy Relaxation and Domain Coarsening

Using Monte Carlo simulations, we have studied the relaxation of energy of the three-dimensional Ising spin-glass model in aging process. Our finite-size-scaling analysis on the isothermal energy decay after the quench suggests strongly that the energy relaxes by coarsening of domain walls in agreement with the droplet theory. We have also evaluated relaxation times required for spin configurations in small systems, which are regarded as isolated droplets, to flip globally. The results support the fundamental assumption of the droplet theory that coarsening of domain walls, in case of spin glasses, is driven by successive nucleation of thermally activated droplets.

cond-mat.dis-nn↗
arXiv1998

Aging Dynamics of an Elastic String Diffusing in a Disordered Media

The aging effects of a 'diffusing glass', a single elastic string diffusing in a two-dimensional disordered media assisted by thermal noise are studied by Monte Carlo (MC) simulations. We find for the first time convincing numerical evidence of non-trivial aging effects both in the linear response against transverse force and the associated correlation function. Our results retain some important predictions of the conventional dynamical mean-field theory (MFT) but also reveal remarkable differences from it.

cond-mat.dis-nn↗
arXiv1996

Aging Processes within One `Pure State' of the SK Model

Monte Carlo simulations on the SK model have been done to investigate aging processes after a rapid quench from $T=\infty$ to the spin-glass phase. The time range of simulations is taken care of so that the system does not surmount free-energy barriers between the pure states which are considered to diverge in the thermodynamic limit. We simulate time evolutions of extensive energy of the system, Parisi's overlap distribution function, auto-correlation and clones-correlation functions, distribution functions of the two correlations, and magnetization induced by the field applied after a certain waiting time. The data simulated exhibit a rich variety of aging phenomena. Most of them can be interpreted in a unified way, though qualitatively, by the scenario of ``growth of quasi-equilibrium domains'' which we will introduce in this work. More surprisingly, they suggest strongly that a basin of attraction of one dominant pure state spans almost an entire phase space of the system with a common time-reversal symmetry.

cond-mat.dis-nn↗
arXiv1996

Hierarchical Diffusion, Aging and Multifractality

We study toy aging processes in hierarchically decomposed phase spaces where the equilibrium probability distributions are multifractal. We found that the an auto-correlation function, survival-return probability, shows crossover behavior from a power law $t^{-x}$ in the quasi-equilibrium regime ($t\ll\tw$) to another power law $t^{-λ}$ ($λ\geq x$) in the off-equilibrium regime ($t\gg\tw$) obeying a simple $t/\tw$ scaling law. The exponents $x$ and $λ$ are related with the so called mass exponents which characterize the multifractality.

cond-mat.dis-nn↗
arXiv1995

Off-Equilibrium Dynamics of 1+1 dimensional Directed Polymer in Random Media

The relaxational dynamics of 1+1 dimensional directed polymer in random potential is studied by Monte Carlo simulation. A series of temperature quench experiments is performed changing waiting times. Clear crossover from quasi-equilibrium behavior to off-equilibrium behavior appears in the dynamical overlap function whose scaling properties are very similar to those found in the 3 dimensional spin-glass model. In the off-equilibrium part, the fluctuation dissipation theorem of the 1st kind which relates the response function to the tilt field with the conjugate correlation function, is found broken. These aging effects are brought about by the very slow growth of quasi-equilibrium domain driven by successive loop-excitations of various sizes, which form complex network structures.

cond-mat↗