arXiv subjects

Masaru Suzuki

Publications and source records attributed to Masaru Suzuki.

12 recordsLinked to original sources

arXiv2022

Simulations of Surface X-ray Diffraction from a Monolayer 4He Film Adsorbed on Graphite

We carried out simulations of crystal truncation rod (CTR) scatterings, i.e., one of the surface X-ray diffraction techniques with atomic resolution, from a monolayer He film adsorbed on graphite. Our simulations reveal that the 00L rod scatterings from the He monolayer exhibit notable intensity modifications for those from a graphite surface in the ranges of approximately L = 0.6 - 1.7 and L = 2.2 - 3.5. The height of the He monolayer from the graphite surface largely affects the CTR scattering profiles, indicating that CTR scatterings have enough sensitivities to determine the surface structure of the various phases in the He layer. In particular, in the incommensurate solid phase, our preliminary experimental data show the intensity modulations that are expected from the present simulations.

cond-mat.other↗

arXiv2021

Structural Study of Adsorbed Helium Films: New Approach with Synchrotron Radiation X-rays

A few atomic layers of helium adsorbed on graphite have been attracting much attention as one of the ideal quantum systems in two dimension. Although previous reports on neutron diffraction have shown fundamental structural information in these systems, there still remain many open questions. Here, we propose surface crystal truncation rod (CTR) scatterings using synchrotron radiation X-rays as a promising method to reveal surface and interface structures of helium films on graphite at temperatures below 2 K, based on the preliminary experimental results on a monolayer of He-4 on a thin graphite. Our estimation on heat generation by X-ray irradiations also suggests that CTR scatterings are applicable to even at system temperatures near 100 mK.

cond-mat.other↗

arXiv2019

Effect of 3He impurities on the mass decoupling of 4He films

We carried out quartz crystal microbalance experiments of a 5 MHz AT-cut crystal for superfluid 4He films on Grafoil (exfoliated graphite) with a small amount of 3He up to 0.40 atoms/nm2. We found that the mass decoupling from oscillating substrate is considerable sensitive even in a small amount of 3He doping. In a 4He film of 29.3 atoms/nm2, we observed a small drop in resonance frequency at T3 of ~0.4 K for a small amplitude, which is attributed to sticking of 3He atoms on the 4He solid atomic layer. For a large amplitude, the 4He solid layer shows a reentrant mass decoupling at TR close to T3. This decoupling can be explained by the suppression of the superfluid counterflow due to the adsorption of 3He atoms on edge dislocations. As the 4He areal density increases, TR shifts to the lower temperature, and vanishes around a 4He film of 39.0 atoms/nm2.

cond-mat.other↗

arXiv2019

Structure of inert layer 4He adsorbed on a mesoporous silica

We have studied the structure of inert layer 4He adsorbed on mesoporous silica (FSM-16), by the vapor pressure and heat capacity measurements. The heat capacity shows a Schottky-like peak due to the excitation of a part of localized solid to fluid. We analyzed the heat capacity over a wide temperature region based on the model including the contribution of the localized solid and excited fluid and clarified that the excited fluid coexists with the localized solid at high temperature. As the areal density approaches the value at which superfluid appears (n_C), the fluid amount is likely to go to zero, suggesting a possibility that the inert layer is solidified just below n_C.

cond-mat.other↗

arXiv2014

Ostwald Ripening in Multiple-Bubble Nuclei

The ostwald ripening of bubbles is studied by molecular dynamics simulations involving up to 679 million Lennard-Jones particles. Many bubbles appear after depressurizing a system that is initially maintained in the pure-liquid phase, and the coarsening of bubbles follows. The self-similarity of the bubble-size distribution function predicted by Lifshitz-Slyozov-Wagner theory is directly confirmed. The total number of bubbles decreases asymptotically as $t^{-x}$ with scaling exponent $x$. As the initial temperature increases, the exponent changes from $x=3/2$ to $1$, which implies that the growth of bubbles changes from interface-limited (the $t^{1/2}$ law) to diffusion-limited (the $t^{1/3}$ law) growth.

physics.flu-dyn↗

arXiv2013

Huge-scale Molecular Dynamics Simulation of Multibubble Nuclei

We have developed molecular dynamics codes for a short-range interaction potential that adopt both the flat-MPI and MPI/OpenMP hybrid parallelizations on the basis of a full domain decomposition strategy. Benchmark simulations involving up to 38.4 billion Lennard-Jones particles were performed on PRIMEHPC FX10, consisting of 4800 SPARC64 IXfx 1.848 GHz processors, at the Information Technology Center of the University of Tokyo, and a performance of 193 teraflops was achieved, which corresponds to a 17.0% execution efficiency. Cavitation processes were also simulated on PRIMEHPC FX10 and SGI Altix ICE 8400EX at the Institute of Solid State Physics of the University of Tokyo, which involved 1.45 billion and 22.9 million particles, respectively. Ostwald-like ripening was observed after the multibubble nuclei. Our results demonstrate that direct simulations of multiscale phenomena involving phase transitions from the atomic scale are possible and that the molecular dynamics method is a promising method that can be applied to petascale computers.

physics.comp-ph↗

arXiv2013

Memory function of turbulent fluctuations in soft-mode turbulence

Modal relaxation dynamics has been observed experimentally to clarify statistical-physical properties of soft-mode turbulence, the spatiotemporal chaos observed in homeotropically aligned nematic liquid crystals. We found a dual structure, dynamical crossover associated with violation of time-reversal invariance, the corresponding time scales satisfying a dynamical scaling law. To specify the origin of the dual structure, the memory function due to non-thermal fluctuations has been defined by a projection-operator method and obtained numerically using experimental results. The results of the memory function suggest that the non-thermal fluctuations can be divided into Markov and non-Markov contributions, the latter is called the turbulent fluctuation (TF). Consequently, the relaxation dynamics is separated into three characteristic stages: bare-friction, early, and late stages. If the dissipation due to TFs dominates over that of the Markov contribution, the bare-friction stage contracts; the early and late stages then configure the dual structure. The memory effect due to TFs results in the time-reversible relaxation at the early stage, and the disappearance of the memory by turbulent mixing leads to a simple exponential relaxation at the late stage. Furthermore, the memory effect due to TFs is shown to originate from characteristic spatial coherency called the patch structure.

cond-mat.soft↗

arXiv2012

Compressed Exponential Relaxation as Superposition of Dual Structure in Pattern Dynamics of Nematic Liquid Crystals

Soft-mode turbulence (SMT) is the spatiotemporal chaos observed in homeotropically aligned nematic liquid crystals, where non-thermal fluctuations are induced by nonlinear coupling between the Nambu-Goldstone and convective modes. The net and modal relaxations of the disorder pattern dynamics in SMT have been studied to construct the statistical physics of nonlinear nonequilibrium systems. The net relaxation dynamics is well-described by a compressed exponential function and the modal one satisfies a dual structure, dynamic crossover accompanied by a breaking of time-reversal invariance. Because the net relaxation is described by a weighted mean of the modal ones with respect to the wave number, the compressed-exponential behavior emerges as a superposition of the dual structure. Here, we present experimental results of the power spectra to discuss the compressed-exponential behavior and the dual structure from a viewpoint of the harmonic analysis. We also derive a relationship of the power spectra from the evolution equation of the modal autocorrelation function. The formula will be helpful to study non-thermal fluctuations in experiments such as the scattering methods.

cond-mat.soft↗

arXiv2012

Glassy dynamics in relaxation of soft-mode turbulence

The autocorrelation function of pattern fluctuation is used to study soft-mode turbulence (SMT), a spatiotemporal chaos observed in homeotropic nematics. We show that relaxation near the electroconvection threshold deviates from the exponential. To describe this relaxation, we propose a compressed exponential appearing in dynamics of glass forming liquids. Our findings suggest that coherent motion contributes to SMT dynamics. We also confirmed that characteristic time is inversely proportional to electroconvection's control parameter.

cond-mat.soft↗

arXiv2011

Active Brownian Motion in Threshold Distribution of a Coulomb Blockade Model

Randomly-distributed offset charges affect the nonlinear current-voltage property via the fluctuation of the threshold voltage of Coulomb blockade arrays. We analytically derive the distribution of the threshold voltage for a model of one-dimensional locally-coupled Coulomb blockade arrays, and propose a general relationship between conductance and the distribution. In addition, we show the distribution for a long array is equivalent to the distribution of the number of upward steps for aligned objects of different height. The distribution satisfies a novel Fokker-Planck equation corresponding to active Brownian motion. The feature of the distribution is clarified by comparing it with the Wigner and Ornstein-Uhlenbeck processes. It is not restricted to the Coulomb blockade model, but instructive in statistical physics generally.

cond-mat.stat-mech↗

arXiv2011

Size Dependence of Current-Voltage Properties in Coulomb Blockade Networks

We theoretically investigate the current-voltage (I-V) property of two-dimensional Coulomb blockade (CB) arrays by conducting Monte Carlo simulations. The I-V property can be divided into three regions and we report the dependence of the aspect ratio delta (namely, the lateral size N_{y} over the longitudinal one N_{x}). We show that the average CB threshold obeys a power-law decay as a function of delta. Its exponent gamma corresponds to a sensitivity of the threshold depending on delta, and is inversely proportional to N_{x} (i.e., delta at fixed N_{y}). Further, the power-law exponent zeta, characterizing the nonlinearity of the I-V property in the intermediate region, logarithmically increases as delta increases. Our simulations describe the experimental result zeta=2.25 obtained by Parthasarathy et al. [Phys. Rev. Lett. 87 (2001) 186807]. In addition, the asymptotic I-V property of one-dimensional arrays obtained by Bascones et al. [Phys. Rev. B. 77 (2008) 245422] is applied to two-dimensional arrays. The asymptotic equation converges to the Ohm's law at the large voltage limit, and the combined tunneling-resistance is inversely proportional to delta. The extended asymptotic equation with the first-order perturbation well describes the experimental result obtained by Kurdak et al. [Phys. Rev. B 57 (1998) R6842]. Based on our asymptotic equation, we can estimate physical values that it is hard to obtain experimentally.

cond-mat.mes-hall↗

arXiv2010

Cumulative distribution functions associated with bubble-nucleation processes in cavitation

Bubble-nucleation processes of a Lennard-Jones liquid are studied by molecular dynamics simulations. Waiting time, which is the lifetime of a superheated liquid, is determined for several system sizes, and the apparent finite-size effect of the nucleation rate is observed. From the cumulative distribution function of the nucleation events, the bubble-nucleation process is found to be not a simple Poisson process but a Poisson process with an additional relaxation time. The parameters of the exponential distribution associated with the process are determined by taking the relaxation time into account, and the apparent finite-size effect is removed. These results imply that the use of the arithmetic mean of the waiting time until a bubble grows to the critical size leads to an incorrect estimation of the nucleation rate.

cond-mat.stat-mech↗