arXiv subjects

Tomoaki Nogawa

Publications and source records attributed to Tomoaki Nogawa.

28 records · Page 2Linked to original sources

arXiv2010

Dynamical Study of Polydisperse Hard-Sphere System

We study the interplay between the fluid-crystal transition and the glass transition of elastic sphere system with polydispersity using nonequilibrium molecular dynamics simulations. It is found that the end point of the crystal-fluid transition line, which corresponds to the critical polydispersity above which the crystal state is unstable, is on the glass transition line. This means that crystal and fluid states at the melting point becomes less distinguishable as polydispersity increases and finally they become identical state, i.e., marginal glass state, at critical polydispersity.

cond-mat.stat-mech↗

arXiv2010

From the Frenkel-Kontorova model to Josephson junction arrays - the Aubry's transition as a jamming-glass transition -

The Frenkel Kontorova (FK) model is known to exhibit the so called Aubry's transition which is a jamming or frictional transition at zero temperature. Recently we found similar transition at zero and finite temperatures in a super-conducting Josephson junction array (JJA) on a square lattice under external magnetic field. In the present paper we discuss how these problems are related.

cond-mat.stat-mech↗

arXiv2009

Reply to Comment on `Monte-Carlo simulation study of the two-stage percolation transition in enhanced binary trees'

We discuss the nature of the two-stage percolation transition on the enhanced binary tree in order to explain the disagreement in the estimation of the second transition probability between the one in our recent paper (J. Phys. A:Math. Theor. 42 (2009) 145001) and the one in the comment to it from Baek, Minnhagen and Kim. We point out some reasons that the finite size scaling analysis used by them is not proper for the enhanced tree due to its nonamenable nature, which is verified by some numerical results.

cond-mat.stat-mech↗

arXiv2009

Vortex stripe glass with self-generated randomness

We found a finite temperature glass transition in the absence of quenched disorder in frustrated Josephson junction arrays (JJA) on a square lattice with anisotropic Josephson couplings by numerical simulations. The vortexes develop zigzag stripes into the direction of weaker coupling at low temperatures. The whole amorphous vortex solid can flow smoothly into the direction of stronger coupling by non-trivial soft modes. As the result the macroscopic phase coherence is destroyed being reminiscent of vortex flow in pure bulk superconductors or spin-chirality decoupling in frustrated magnets. On the contrary such soft-modes are absent into the direction of weaker coupling. Consequently the system behaves as a Ohmic (unjammed) liquid or superconducting (jammed) solid with respect to injection of external electric current, i. e. shear, along different directions. This jamming-glass transition can be regarded as a two dimensional realization of the Aubry's transition.

cond-mat.supr-con↗

arXiv2009

Monte-Carlo simulation study of the two-stage percolation transition in enhanced binary trees

We perform Monte-Carlo simulations to study the Bernoulli ($p$) bond percolation on the enhanced binary tree which belongs to the class of nonamenable graphs with one end. Our numerical results show that the system has two different percolation thresholds $p_{c1}$ and $p_{c2}$. All the points in the intermediate phase $(p_{c1} < p < p_{c2})$ are critical and there exist infinitely many infinite clusters in the intermediate phase. In this phase the corresponding fractal exponent continuously increases with $p$ from zero to unity.

cond-mat.stat-mech↗

arXiv2008

Vortex jamming in superconductors and granular rheology

We demonstrate that a highly frustrated anisotropic Josephson junction array(JJA) on a square lattice exhibits a zero-temperature jamming transition, which shares much in common with those in granular systems. Anisotropy of the Josephson couplings along the horizontal and vertical directions plays roles similar to normal load or density in granular systems. We studied numerically static and dynamic response of the system against shear, i. e. injection of external electric current at zero temperature. Current-voltage curves at various strength of the anisotropy exhibit universal scaling features around the jamming point much as do the flow curves in granular rheology, shear-stress vs shear-rate. It turns out that at zero temperature the jamming transition occurs right at the isotropic coupling and anisotropic JJA behaves as an exotic fragile vortex matter : it behaves as superconductor (vortex glass) into one direction while normal conductor (vortex liquid) into the other direction even at zero temperature. Furthermore we find a variant of the theoretical model for the anisotropic JJA quantitatively reproduces universal master flow-curves of the granular systems. Our results suggest an unexpected common paradigm stretching over seemingly unrelated fields - the rheology of soft materials and superconductivity.

cond-mat.stat-mech↗

arXiv2008

Abnormal diffusion of a single vortex in the two dimensional XY model

We study thermal diffusion dynamics of a single vortex in two dimensional XY model. By numerical simulations we find an abnormal diffusion such that the mobility decreases with time $t$ as $1/\ln t$. In addition we construct a one dimensional diffusion-like equation to model the dynamics and confirm that it conserves quantitative property of the abnormal diffusion. By analyzing the reduced model, we find that the radius of the collectively moving region with the vortex core grows as $R(t) \propto t^{1/2}$. This suggests that the mobility of the vortex is described by dynamical correlation length as $1/\ln R(t)$.

cond-mat.supr-con↗

arXiv2008

Spatio-temporal scaling for out-of-equilibrium relaxation dynamics of an elastic manifold in random media: crossover between the Larkin regime and thermally activated regime

We study relaxation dynamics of a three dimensional elastic manifold in random potential from a uniform initial condition by numerically solving the Langevin equation.We observe growth of roughness of the system up to larger wavelengths with time.We analyze structure factor in detail and find a compact scaling ansatz describing two distinct time regimes and crossover between them. We find short time regime corresponding to length scale smaller than the Larkin length $L_c$ is well described by the Larkin model which predicts a power law growth of domain size $L(t)$. Longer time behavior exhibits the random manifold regime with slower growth of $L(t)$.

cond-mat.dis-nn↗

arXiv2006

Nonequilibrium relaxation analysis of a quasi-one-dimensional frustrated XY model for charge-density waves in ring-shaped crystals

We propose a model for charge density waves in ring shaped crystals, which depicts frustration between intra- and inter-chain couplings coming from cylindrical bending. It is then mapped to a three dimensional uniformly frustrated XY model with one dimensional anisotropy in connectivity. The nonequilibrium relaxation dynamics is investigated by Monte Carlo simulations to find a phase transition which is quite different from that of usual whisker crystal. We also find that the low temperature state is a three dimensional phase vortex lattice with a two dimensional phase coherence in a cylindrical shell and the system shows power law relaxation in the ordered phase.

cond-mat.stat-mech↗

arXiv2005

Possibility of the Solid-Fluid Transition in Moving Periodic Systems

The steady sliding state of periodic structures such as charge density waves and flux line lattices is numerically studied based on two and three dimensional driven random field XY models. We focus on the dynamical phase transition between plastic flow and moving solid phases controlled by the magnitude of the driving force. By analyzing the connectivity of co-moving clusters, we find that they percolate the system within a finite observation time under driving forces larger than a certain critical force. The critical force, however, logarithmically diverges with the observation time, i.e. the moving solid phase exhibits only within a certain finite time, which exponentially grows with the driving force.

cond-mat.dis-nn↗