arXiv subjects

Kota Mitsumoto

Publications and source records attributed to Kota Mitsumoto.

12 recordsLinked to original sources

arXiv2026

Starvation suppression in dense scale-free metabolic networks: Dynamical mean-field analysis of catalytic reaction networks

Cellular metabolic networks exhibit scale-free topologies with power-law degree distributions across diverse organisms. Although such topologies are often linked to mutational robustness and evolutionary advantage, their role in metabolic dynamics remains unclear. Using dynamical mean-field theory, we derive an exact solution for an intracellular catalytic reaction model on dense random networks with arbitrary degree distributions. We show that the metabolic-starvation transition observed under nutrient-poor conditions for homogeneous degree distributions disappears when the out-degree distribution is scale-free. We also show a power-law in-degree distribution of the underlying catalytic reaction network gives rise to a power-law distribution of biomolecular abundances with the same exponent. Large-scale numerical simulations validate these predictions. Our results provide a theoretical framework linking network topology and metabolic dynamics.

cond-mat.stat-mech↗

arXiv2026

Theory of clusterization in orbitally degenerate transition-metal compounds driven by lattice instabilities

We derive an effective orbital-lattice model with quantum $S=1$ degrees of freedom for transition-metal compounds, providing a microscopic understanding of cluster formation driven by the cooperative interplay of spin, orbital, and lattice degrees of freedom. Motivated by the trimerized phases observed in LiVS$_2$ and LiVO$_2$, we consider a triangular-lattice three-orbital system with two electrons per site occupying the threefold-degenerate $t_{2g}$ manifold. Starting from a multiorbital Kanamori-Hubbard Hamiltonian, we project the low-energy sector onto the local $S=1$ triplet manifold, in which two electrons occupy different orbitals according to Hund's coupling. The resulting effective model exhibits exchange networks whose geometry is determined by the orbital configuration. However, the orbital-driven exchange interactions alone do not stabilize the experimentally observed trimer phase. We find that by incorporating ionic lattice displacements that modulate transfer integrals and induce bond-dependent exchange couplings on shortened and elongated bonds, the phase competition is qualitatively altered, leading to the robust stabilization of a trimerized ground state within a fully quantum-mechanical framework. We further show that a simplified orbital-lattice model, in which the spin-exchange energy is replaced by effective bond energies, faithfully reproduces the essential ground-state properties of the microscopic model. This reduced description enables large-scale finite-temperature simulations and reveals a rich sequence of thermal phase transitions, including first-order, second-order, and Kosterlitz-Thouless transitions into distinct spin-, orbital-, and lattice-ordered phases.

cond-mat.str-el↗

arXiv2025

Elastic heterogeneity governs anomalous scaling in a soft porous crystal

Nanoscale molecular transport plays a crucial role in regulating mass diffusion and responsiveness in condensed matter systems. In soft porous crystals, in particular, adsorption of guest molecules induces host framework deformation and changes in rigidity, underpinning their characteristic stimuli-responsive behaviour. Surface-mediated adsorption leads to inhomogeneous adsorbate distribution, which, through local framework deformation, induces spatial variations in rigidity -- elastic heterogeneity. Although this heterogeneity is expected to affect adsorption kinetics and mechanical behaviour, its role remains poorly understood. Here we show that elastic heterogeneity governs adsorption kinetics, leading to emergent phenomena including size-dependent uptake, surface creasing, and anomalous dynamic scaling that is distinct from established scaling. Stress relaxation near corners facilitates adsorption, resulting in a size-dependent deviation from diffusive kinetics. Away from corners, flexible unadsorbed regions between rigid adsorbed domains relieve stress through crease formation. The resulting lateral correlations exhibit anomalous dynamic scaling, characterized by a breakdown of scale invariance between global and local interfacial fluctuations. These findings provide a mechanistic foundation for controlling adsorption and deformation kinetics in soft porous materials via elastic heterogeneity. Our work opens a route to engineering responsive materials, where mechanical feedback is harnessed to control cooperative molecular transport and drive macroscopic shape changes under external perturbations.

cond-mat.soft↗

arXiv2024

Diffusionless relaxation of half-skyrmion liquid, hexatic, and crystalline states in a chiral molecular crystal

Particles in a crowded environment exhibit slow anomalous diffusion, and their efficient manipulation is important in controlling transport phenomena in complex materials. Skyrmions and half-skyrmions, spatially localized quasiparticles observed in magnetic systems and liquid crystals, also exhibit diffusive motion. They exhibit normal diffusion in dilute conditions. However, the cooperative dynamics and diffusion of skyrmions and half-skyrmions in their condensed liquid, hexatic, and crystalline phases are elusive. Here we show in the half-skyrmion condensed phases that the fusion and fission of half-skyrmions, not their diffusion, are responsible for the primary structural relaxation. The fusion and fission occur due to the non-conserved nature of the quasiparticle number density. The diffusion, which contributes to the secondary structural relaxation, is suppressed by cages formed by surrounding half-skyrmions, whereas enhanced by Mermin-Wagner fluctuation characteristic to two-dimensional systems, leading to subdiffusive motion. Large displacement of half-skyrmions is locally excited by fusion-fission and bond-breaking between adjacent half-skyrmions via heterogeneous elastic fields. Furthermore, the motion of half-skyrmions couples with transverse and longitudinal sound wave excitation differently, where the transverse sound wave is more attenuated than the longitudinal one due to the coupling between transverse sound wave and half-skyrmion deformation. We also discuss the {relationship} between half-skyrmion diffusion in our system and skyrmion diffusion in magnetic systems. Our result provides a qualitative difference in dynamical properties between half-skyrmion gaseous and condensed phases, suggesting the efficient manipulation of high-density half-skyrmions and skyrmions.

cond-mat.soft↗

arXiv2023

Adsorption superlattice stabilized by elastic interactions in a soft porous crystal

We numerically show that molecules adsorbed in a soft porous crystal form a superlattice (SL) stabilized by elastic interactions. In a mechanically flexible honeycomb lattice model, when the elastic interactions between the next nearest neighboring lattice sites are strong, a long-range ordered 1/3-filling SL state emerges. By calculating the thermodynamic stability, it is found that the SL state is robust against thermal fluctuation. Our results provide a mechanism of elasticity-driven SL formation, which can be utilized for controlling the distribution of adsorbed molecules.

cond-mat.soft↗

arXiv2023

Elastic heterogeneity governs asymmetric adsorption-desorption in a soft porous crystal

Metal--organic frameworks (MOFs), which possess a high degree of crystallinity and a large surface area with tunable inorganic nodes and organic linkers, exhibit high stimuli-responsiveness and molecular adsorption selectivity that enable various applications. The adsorption in MOFs changes the crystalline structure and elastic moduli. Thus, the coexistence of adsorbed/desorbed sites makes the host matrices elastically heterogeneous. However, the role of elastic heterogeneity in the adsorption--desorption transition has been overlooked. Here we show the asymmetric role of elastic heterogeneity in the adsorption--desorption transition. We construct a minimal model incorporating adsorption-induced lattice expansion/contraction and an increase/decrease in the elastic moduli. We discover that the transition is hindered by the entropic and energetic effects which become asymmetric in adsorption process and desorption process, leading to the strong hysteretic nature of the transition. Furthermore, the adsorbed/desorbed sites exhibit spatially heterogeneous domain formation, implying that the domain morphology and interfacial area between adsorbed/desorbed sites can be controlled by elastic heterogeneity. Our results provide a theoretical guideline for designing soft porous crystals with tunable adsorption hysteresis and the dispersion and domain morphology of adsorbates using elastic heterogeneity.

cond-mat.soft↗

arXiv2023

Replica theory for disorder-free spin-lattice glass transition on a tree-like simplex network

A class of pyrochlore oxides, $A_2$Mo$_2$O$_7$ ($A =$ Ho, Y, Dy, Tb) with magnetic ions on corner-sharing tetrahedra is known to exhibit spin-glass transitions without appreciable amount of quenched disorder. Recently a disorder-free theoretical model for such a system has been proposed which takes into account not only spins but also lattice distortions as dynamical variables [K. Mitsumoto, C. Hotta and H. Yoshino, Phys. Rev. Lett. 124, 087201 (2020)]. In the present paper we develop and analyze an exactly solvable disorder-free mean-field model which is a higher-dimensional counterpart of the model. We find the system exhibit complex free-energy landscape accompanying replica symmetry breaking through the spin-lattice coupling.

cond-mat.dis-nn↗

arXiv2022

Supercooled Jahn-Teller Ice

When the spins on the frustrated pyrochlore lattice obey the celebrated 2-$in$-2-$out$ ice rule, they stay in a correlated disordered phase and break the third law of thermodynamics. Similarly, if the atomic ions on the pyrochlore lattice move in and outward of the tetrahedra, they may obey a constraint resembling the ice rule. We discover that a model for pyrochlore molybdates $A_2$Mo$_2$O$_7$ ($A=$Y, Dy, Tb) exhibits a "supercooled ice" state of the displacement degrees of freedom of Mo$^{4+}$ ions, when we take account of the Jahn-Teller (JT) effect. The JT effect occurs when the lattice distortions reduce the symmetry of the local crystal field, resulting in the orbital-energy-splitting that causes the local energy gain. Unlike the standard JT effect that leads to periodic long range ordering, the displacements of Mo$^{4+}$ ions are disordered following the ice-like rule. We microscopically derive a model that describes this situation by having the 2nd and 3rd neighbor interactions between in-out lattice displacements comparably as strong as the nearest neighbor interactions of standard ice. There, the well-known nearly flat energy landscape of the ice state is altered to a metastable highly quasi-degenerate ice-like liquid state coexisting with a crystalline-like ground state. Our Monte Carlo simulations show that this liquid remains remarkably stable down to low temperatures by avoiding the putative first order transition. The relaxation in the supercooled JT ice state exhibits glassy dynamics with a plateau structure. They fit the feature of a "good glassformer" very often found in molecular liquids, but that has never been observed in material solids. The high glass-forming ability of the interacting lattice degrees of freedom will play a key role in the spin-glass transition of the material.

cond-mat.str-el↗

arXiv2022

Skyrmion crystal in the RKKY system on the two-dimensional triangular lattice

We study the ordering properties of the isotropic RKKY Heisenberg model on the two-dimensional (2D) triangular lattice by extensive Monte Carlo simulations to get insights into the chiral-degenerate skyrmion crystal (SkX) of metallic magnets. Our Hamiltonian contains only the spin-quadratic RKKY interaction derived from the spherical Fermi surface, containing neither the nesting nor the many-body interaction. The SkX phase is stabilized under applied fields where the frustration associated with the oscillating nature of the RKKY interaction and the emergent many-body interactions generated by thermal fluctuations play important roles. Replica symmetry breaking, reported in our recent study on the 3D RKKY model [Phys. Rev. B 104, 184432 (2021)], turns out to be absent in the present 2D model. Implications to the SkX formation mechanism are discussed.

cond-mat.str-el↗

arXiv2021

Replica symmetry breaking in the RKKY skyrmion crystal system

We study the RKKY Heisenberg model on a three-dimensional stacked-triangular lattice under magnetic fields by extensive Monte Carlo simulations to get insight into the chiral-degenerate symmetric skyrmion crystal (SkX) in centrosymmetric metallic magnets. The triple-$q$ SkX state and the double-$q$ states are realized, together with the single-$q$ state. We find an unexpected phenomenon of the replica-symmetry breaking (RSB) well-known in glassy systems, although the Hamiltonian and the ordered state are entirely regular. In the RSB SkX phase, the triple-$q$ SkX state macroscopically coexists with the single-$q$ state, in spite of the fact that these ordered states cannot be transformed via any Hamiltonian-symmetry operation. In the thermodynamic limit, the free energies of these states are degenerate whereas the free-energy barrier between the states diverges, breaking the ergodicity. A similar RSB is observed also in the RSB double-$q$ phase where the double-$q$ state macroscopically coexists with the single-$q$ state. Experimental implications are discussed.

cond-mat.str-el↗

arXiv2020

Spin-orbital glass transition in a model of a frustrated pyrochlore magnet without quenched disorder

We show theoretically that spin and orbital degrees of freedom in the pyrochlore oxide Y2Mo2O7, which is free of quenched disorder, can exhibit a simultaneous glass transition, working as dynamical randomness to each other. The interplay of spins and orbitals is mediated by the Jahn-Teller lattice distortion that selects the choice of orbitals, which then generates variant spin exchange interactions ranging from ferromagnetic to antiferromagnetic ones. Our Monte Carlo simulations detect the power-law divergence of the relaxation times and the negative divergence of both the magnetic and dielectric non-linear susceptibilities, resolving the long-standing puzzle on the origin of the disorder-free spin glass.

cond-mat.dis-nn↗

arXiv2018

Orientational ordering of closely packed Janus particles

We study orientational ordering of $2$-dimensional closely packed Janus particles by extensive Monte Carlo simulations. For smaller patch sizes the system remains in the plastic crystal phase where the rotational degrees of freedom are disordered down to the lowest temperatures. There the liquid consist of dimers and trimers of the attractive patches. For large enough patch sizes, the system exhibits a thermodynamic transition into a phase with stripe patterns of the patches breaking the three-fold rotational symmetry. Our results strongly suggests that the latter is a 2nd order phase transition whose universality is the same as that of the $3$-state Potts model in $2$-dimensions. Furthermore we analyzed the relaxation dynamics of the system performing quenching simulations into the stripe phase. We found growing domains of the stripes. The relaxation of key dynamical quantities follow universal scaling features in terms of the domain size.

cond-mat.soft↗