arXiv subjects

Hideyuki Mizuno

Publications and source records attributed to Hideyuki Mizuno.

At least 19 recordsLinked to original sources

arXiv2026

Continuum model for the terahertz dielectric response of glasses

Boson peak dynamics in glasses produce a robust crossover in the terahertz (THz) dielectric response that standard Debye or Lorentz models do not capture. We develop a continuum description of this THz response, coupling an infrared-effective charge fluctuation spectrum to a frequency-dependent shear modulus, and apply it to glycerol glass. The model reproduces the measured complex dielectric function and the nearly linear infrared light-vibration coupling around the boson peak, and it highlights the dominant role of transverse shear dynamics.

cond-mat.dis-nn↗

arXiv2026

Cohesion-induced hysteresis and breakdown of marginal stability in jammed granular materials

The dependence of mechanical properties on microscopic interactions remains a central problem in the physics of disordered solids near the jamming transition. We numerically and theoretically investigate the mechanical response of jammed cohesive granular materials using discrete element simulations and effective medium theory (EMT). We find that the shear modulus exhibits pronounced hysteresis under compression and decompression, even though the interparticle force law itself is strictly history-independent. While such hysteresis disappears for purely repulsive particles when mechanical properties are characterized in terms of pressure, it persists in cohesive packings, indicating that pressure is not a unique state variable for cohesive particles. Extending EMT to cohesive interactions, we show that the functional form of the shear modulus remains the same for both repulsive and cohesive particles, but that attractive interactions violate marginal stability. The resulting deviation from marginal stability generates excess rigidity, as predicted by a scaling relation. This prediction is quantitatively verified by numerical simulations and explains the persistent hysteresis in cohesive packings.

cond-mat.soft↗

arXiv2026

Critical fluctuations of elastic moduli in jammed solids

We investigate sample-to-sample fluctuations of the shear modulus in ensembles of particle packings near the jamming transition. Unlike the average modulus, which exhibits distinct scaling behaviours depending on the interparticle potential, the fluctuations obey a critical exponent that is independent of the potential. Furthermore, this scaling behaviour has been confirmed in two-dimensional packings, indicating that it holds regardless of spatial dimension. Using this scaling law, we discuss the relationship predicted by heterogeneous-elasticity theory between elastic-modulus fluctuations and the Rayleigh scattering of sound waves across different pressures. Our numerical results provide a useful foundation for developing a unified theoretical description of the jamming critical phenomenon.

cond-mat.soft↗

arXiv2026

Boson peak in the dynamical structure factor of network- and packing-type glasses

Glasses are structurally disordered solids that host, in addition to crystalline-like phonons, vibrational excitations with no direct phononic counterpart. A long-standing universal signature is the excess vibrational density of states~(vDOS) over the Debye prediction, known as the boson peak~(BP), which has been extensively reported via inelastic neutron and X-ray scattering measurements of the dynamical structure factor $S(q,ω)$. Here we quantify the vDOS directly from dynamical-structure-factor data and clarify the microscopic origin of the BP. We contrast two routes to extract the vDOS from $S(q,ω)$: (i) using high-wavenumber $q$ data beyond the Debye wavenumber $q_D$ to access predominantly incoherent scattering and recover the vDOS in a manner analogous to velocity-autocorrelation-based approaches; and (ii) integrating $S(q,ω)$ over the low-$q$ regime below $q_D$, which enables a decomposition of the vDOS into contributions from distinct wavenumber sectors and thereby provides direct access to the spatial character of vibrational modes. Focusing on the second route, we demonstrate that the BP in the vDOS emerges as the spectral consequence of a dispersionless excitation band in $S(q,ω)$. Our main results are obtained from molecular-dynamics simulations, and we further show that the same mechanism is captured by an effective-medium theory for random spring networks, providing a unified interpretation that connects the excess vDOS to the wavenumber-resolved structure of vibrational excitations in glasses.

cond-mat.soft↗

arXiv2025

Boson peak in covalent network glasses: Isostaticity and marginal stability

The boson peak (BP) stands as a key feature in understanding glasses and amorphous materials. It directly underlies their anomalous material properties, including thermal behaviors such as excess specific heat and low thermal conductivity, as well as mechanical characteristics such as nonaffine elasticity and fragile plasticity. Despite its importance, understanding of the BP remains limited in covalent network glasses. The most promising concepts are isostaticity and marginal stability, which have been established in theories of rigidity percolation and the jamming transition. While these concepts, supported by comprehensive data, account for the BP in packing-based glasses, comparable explanations have not yet been demonstrated for covalent network glasses. Here we study silica glass, a prototypical covalent network glass, using molecular dynamics simulations. We show that the BP in silica glass is governed by near-isostatic constraints and marginal stability, supporting their universality across diverse glassy systems. Furthermore, we reveal that these principles manifest as a wavenumber-independent band in the dynamical structure factor, and we demonstrate consistency with inelastic X-ray scattering data on silica glass. Our results provide a unified, experimentally testable framework for deciphering the BP and for refining the interpretation of scattering data in amorphous materials.

cond-mat.dis-nn↗

arXiv2025

Enhanced collective vibrations in granular materials

Granular materials are defined as collections of macroscopic dissipative particles. Although these systems are ubiquitous in our lives, the nature and the causes of their non-trivial collective dynamics still remain elusive and have attracted significant interest in non-equilibrium physics. Here, we focus on the vibrational dynamics of granular materials. While the vibrational dynamics of random packings have been examined concerning the jamming transition, previous research has overlooked the role of contact dissipations. We conducted numerical and analytical investigations into the vibrational dynamics of random packings influenced by the normal dissipative force, which is the simplest model for contact dissipations. Our findings reveal that the kinetic energy per mode diverges in the low-frequency range, following the scaling law $\mathcal{K}_l \propto ω^{-2}_l$ with the frequency $ω_l$, indicating that low-frequency modes experience strong excitation and that the equipartition of energy is violated. Additionally, the spatial structure factor of the velocity field displays the scaling law $S_v(q) \propto q^{-2}$ with the wavenumber $q$, which signifies that the velocity field has an infinitely long range. We demonstrate that these phenomena arise from the effects of weaker damping on softer modes, where the particle displacements parallel to the contacts are minimal in the low-frequency modes, rendering normal dissipation ineffective at dampening these modes.

cond-mat.soft↗

arXiv2025

Persistent homology elucidates hierarchical structures responsible for mechanical properties in covalent amorphous solids

Understanding how atomic-level structures govern the mechanical properties of amorphous materials remains a fundamental challenge in solid-state physics. Under mechanical loading, amorphous materials exhibit simple affine and spatially inhomogeneous nonaffine displacements that contribute to the elastic modulus through the Born (affine) and nonaffine terms, respectively. The differences between soft local structures characterized by small Born terms or large nonaffine displacements have yet to be elucidated. This challenge is particularly complex in covalent amorphous materials such as silicon, where the medium-range order (MRO) plays a crucial role in the network structure. To address these issues, we combined molecular dynamics simulations with persistent homology analysis. Our results reveal that local structures with small Born terms are governed by short-range characteristics, whereas those with large nonaffine displacements exhibit hierarchical structures in which short-range disorder is embedded within the MRO. These hierarchical structures are also strongly correlated with low-energy localized vibrational excitations. Our findings demonstrate that the mechanical responses and dynamic properties of covalent amorphous materials are intrinsically linked to the MRO, providing a new framework for understanding and tailoring their properties.

cond-mat.mtrl-sci↗

arXiv2025

Relationship between the boson peak and first sharp diffraction peak in glasses

Boson peak (BP) dynamics refers to the universal excitation in the terahertz region of glass. In this study, the universal dynamics of BP were quantitatively evaluated in various glassy materials based on the heterogeneous elasticity theory (HET), and the determinants of BP were successfully extracted. A strong correlation was observed between the maximum possible coarse-graining wavenumber, which is a determinant of the BP in the HET, and the first sharp diffraction peak (FSDP) wavenumber, which is a characteristic index of the medium-range order in glasses. The results indicate that the behaviour of BP in glass can be quantitatively understood in the following two steps. First, the FSDP representing the largest structural correlation in glass is dominantly used to determine the unit size of the elastic modulus heterogeneity, and second, the magnitude of the elastic modulus fluctuation is used to determine the frequency and intensity of the BP.

cond-mat.dis-nn↗

arXiv2024

Avalanche criticality emerges by thermal fluctuation in a quiescent glass

We report avalanche criticality of thermal relaxation in glassy systems after a rapid quench by molecular simulation. Our analysis of the energy landscape and the scaling reveals that particle rearrangement is critical. The critical phenomenon has the same origin as avalanches in sheared amorphous solids, but the critical exponent differs from previously observed. Our results suggest that by viewing a glass as a thermally driven elastoplastic material, we can understand dynamics below the glass transition point, such as aging.

cond-mat.soft↗

arXiv2024

Effective medium theory for viscoelasticity of soft jammed solids

The viscoelastic properties of soft jammed solids, such as foams, emulsions, and soft colloids, have been the subject of experiments, with particular interest in the anomalous viscous loss. However, a microscopic theory to explain these experimental results is still lacking. Here, we develop an effective medium theory that incorporates the effects of contact damping. The theory explains experimentally observed viscoelastic properties, particularly attributing the anomalous viscous loss to marginal stability in amorphous systems. This work establishes a microscopic theory for describing the impact of damping on soft jammed solids and their viscoelastic behaviors.

cond-mat.soft↗

arXiv2024

Structural fluctuations in active glasses

The glassy dynamics of dense active matter have recently become a topic of interest due to their importance in biological processes such as wound healing and tissue development. However, while the liquid-state properties of dense active matter have been studied in relation to the glass transition of active matter, the solid-state properties of active glasses have yet to be understood. In this work, we study the structural fluctuations in the active glasses composed of self-propelled particles. We develop a formalism to describe the solid-state properties of active glasses in the harmonic approximation limit and use it to analyze the displacement fields in the active glasses. Our findings reveal that the dynamics of high-frequency normal modes become quasi-static with respect to the active forces, and consequently, excitations of these modes are significantly suppressed. This leads to a violation of the equipartition law, suppression of particle displacements, and the apparent collective motion of active glasses. Overall, our results provide a fundamental understanding of the solid-state properties of active glasses.

cond-mat.soft↗

arXiv2024

Universal mechanism of shear thinning in supercooled liquids

Soft glassy materials experience a significant reduction in viscosity $η$ when subjected to shear flow, known as shear thinning. This phenomenon is characterized by a power-law scaling of $η$ with the shear rate $\dotγ$, $η\propto \dotγ^{-ν}$, where the exponent $ν$ is typically around $0.7$ to $0.8$ across different materials. Two decades ago, the mode coupling theory (MCT) suggested that shear thinning occurs due to the advection. However, it predicts too large $ν= 1$ (> $0.7$ to $0.8$) and overestimates the onset shear rate by orders of magnitude. Recently, it was claimed that a minute distortion of the particle configuration is responsible for shear thinning. Here we extend the MCT to include the distortion, and find that both advection and distortion contribute to shear thinning, but the latter is dominant. Our formulation works quantitatively for several different glass formers. We explain why shear thinning is universal for many glassy materials.

cond-mat.soft↗

arXiv2024

Unified study of viscoelasticity and sound damping in hard and soft amorphous solids

Recent research has made significant progress in understanding the non-phonon vibrational states present in amorphous materials. It has been established that their vibrational density of states follows non-Debye scaling laws. Here, we show that the non-Debye scaling laws play a crucial role in determining material properties of a broad range of amorphous solids, from ``hard" amorphous solids like structural glasses to ``soft" amorphous solids such as foams and emulsions. We propose a unified framework of viscoelasticity and sound damping for these materials. Although these properties differ significantly between hard and soft amorphous solids, they are determined by the non-Debye scaling laws. We also validate our framework using numerical simulations.

cond-mat.soft↗

arXiv2024

Instantaneous normal modes of glass-forming liquids during the athermal relaxation process of the steepest descent algorithm

Understanding glass formation by quenching remains a challenge in soft condensed matter physics. Recent numerical studies on steepest descent dynamics, which is one of the simplest models of quenching, revealed that quenched liquids undergo slow relaxation with a power law towards mechanical equilibrium and that the late stage of this process is governed by local rearrangements of particles. These advances motivate the detailed study of instantaneous normal modes during the relaxation process because the glassy dynamics is considered to be governed by stationary points of the potential energy landscape. Here, we performed a normal mode analysis of configurations during the steepest descent dynamics and found that the dynamics is driven by almost flat directions of the potential energy landscape at long times. These directions correspond to localized modes and we characterized them in terms of their statistics and structure using methods developed in the study of local minima of the potential energy landscape.

cond-mat.soft↗

arXiv2023

Heterogeneity and Low-Frequency Vibrations in Bidisperse Sphere Packings

In the jamming transition of monodisperse packings, spatial heterogeneity is irrelevant as the transition is described by mean-field theories. Here, we show that this situation drastically changes if the particle-size dispersity is large enough. We use computer simulations to study the structural and vibrational properties of bidisperse sphere packings with a large size ratio. Near the critical point, the small particles tend to form clusters, leading to the emergence of large-scale structural heterogeneity. Concomitantly, the low-frequency vibrations are significantly enhanced compared to those in monodisperse packings, and their density of states follows a linear law with the frequency. We numerically and theoretically demonstrate that these behaviors of the structural heterogeneity and the low-frequency vibrations are intimately connected. The present work suggests that the nature of heterogeneous packings is markedly different from that of homogeneous packings.

cond-mat.soft↗

arXiv2023

Scale Separation of Shear-induced Criticality in Glasses

In a sheared steady state, glasses reach a nonequilibrium criticality called yielding. In this letter, we report that the qualitative nature of this nonequilibrium critical phenomenon depends on the details of the system and that responses and fluctuations are governed by different critical correlation lengths in specific situations. This scale separation of critical lengths arises when the screening of elastic propagation of mechanical signals is not negligible. We also explain that the impact of the screening effects is crucially determined by the microscopic dissipation mechanism.

cond-mat.soft↗

arXiv2023

Microrheology near jamming

The jamming transition is a nonequilibrium critical phenomenon, which governs characteristic mechanical properties of jammed soft materials, such as pastes, emulsions, and granular matters. Both experiments and theory of jammed soft materials have revealed that the complex modulus measured by conventional macrorheology exhibits a characteristic frequency dependence. Microrheology is a new type of method to obtain the complex modulus, which transforms the microscopic motion of probes to the complex modulus through the generalized Stokes relation (GSR). Although microrheology has been applied to jammed soft materials, its theoretical understanding is limited. In particular, the validity of the GSR near the jamming transition is far from obvious since there is a diverging length scale $l_c$, which characterizes the heterogeneous response of jammed particles. Here, we study the microrheology of jammed particles by theory and numerical simulation. First, we develop a linear response formalism to calculate the response function of the probe particle, which is transformed to the complex modulus via the GSR. Then, we apply our formalism to a numerical model of jammed particles and find that the storage and loss modulus follow characteristic scaling laws near the jamming transition. Importantly, the observed scaling law coincides with that in macrorheology, which indicates that the GSR holds even near the jamming transition. We rationalize this equivalence by asymptotic analysis of the obtained formalism and numerical analysis on the displacement field of jammed particles under a local perturbation.

cond-mat.soft↗

arXiv2023

Avalanche Interpretation of the Power-Law Energy Spectrum in Three-Dimensional Dense Granular Flow

Turbulence is ubiquitous in nonequilibrium systems, and it has been noted that even dense granular flows exhibit characteristics that are typical of turbulent flow, such as the power-law energy spectrum. However, studies on the turbulent-like behavior of granular flows are limited to two-dimensional (2D) flow. We demonstrate that the statistics in three-dimensional (3D) flow are qualitatively different from those in 2D flow. We also elucidate that avalanche dynamics can explain this dimensionality dependence. Moreover, we define clusters of collectively moving particles that are equivalent to vortex filaments. The clusters unveil complicated structures in 3D flows that are absent in 2D flows.

cond-mat.soft↗