arXiv subjects

Kentaro Nomura

Publications and source records attributed to Kentaro Nomura.

At least 19 recordsLinked to original sources

arXiv2026

Scalar-spin-chirality-driven fractional Chern insulator on a kagome lattice

Fractional Chern insulators (FCIs) are the lattice analogs of the fractional quantum Hall states, emerging even without an external magnetic field. In this work, we demonstrate the emergence of the FCI states in a kagome magnet with a noncoplanar magnetic order that induces a finite scalar spin chirality. By incorporating in our model both electron-electron interactions and the effect of band dispersion, we find that stronger interactions relative to the band dispersion stabilize the FCI state over a broader range of scalar spin chirality. We characterize the emergent FCI state by calculating overlap with representative states, identifying the ground-state degeneracy and the finite energy gap in the thermodynamic limit, and tracking the spectral flow under multiple flux-quantum insertions. Our results suggest that kagome magnets with scalar spin chirality can be promising platforms for realizing FCIs.

cond-mat.mes-hall↗

arXiv2026

Social Reality Construction via Active Inference: Modeling the Dialectic of Conformity and Creativity

Social agents both internalize collective norms and reshape them through creative action, yet computational models have not captured this bidirectional process within a unified framework. We propose a multi-agent simulation model grounded in active inference that formalizes the dialectical constitution of social reality on a structured social network. Each agent maintains an internal generative model, communicates with neighbors to form social priors, creates novel observations, and selectively incorporates others' creations into memory. Simulation experiments demonstrate three main findings. First, informationally cohesive social groups emerge endogenously, with representational alignment mirroring the cluster topology of the underlying network. Second, a circular mutual constitution arises between social representations and the observation distribution, maintained through agents' creative acts that project representational structure onto the external world. Third, the propagation of creations exhibits selective, heterogeneous patterns distinct from the stable diffusion of social representations, indicating that agents construct cultural niches through local interaction dynamics. These results suggest that the interplay between social conformity and creative deviation can give rise to the endogenous formation and differentiation of shared social reality.

cs.MA↗

arXiv2026

Repulsive-Interaction-Driven Topological Superconductivity in a Landau Level Coupled to an $s$-Wave Superconductor

A two-dimensional topologically nontrivial state of noninteracting electrons, such as the surface state of a three-dimensional topological insulator, is predicted to realize a topological superconductor when proximity-coupled to an ordinary $s$-wave superconductor. In contrast, noninteracting electrons partially occupying a Landau level, with Rashba spin-orbit coupling that lifts the spin degeneracy, fail to develop topological superconductivity under similar proximity coupling in the presence of the conventional Abrikosov vortex lattice. We demonstrate, through exact diagonalization, that introducing in this model a repulsive interaction between electrons induces topological superconductivity at half-filled Landau level for a range of parameters. This appears rather surprising because a repulsive interaction is expected to inhibit, not promote, pairing, but suggests an appealing principle for realizing topological superconductivity: proximity-coupling a composite Fermi liquid to an ordinary $s$-wave superconductor.

cond-mat.str-el↗

arXiv2026

Magnetic Weyl semimetals: Interplay of band topology and magnetism

We review recent theoretical and experimental developments in magnetic Weyl semimetals, focusing on the electromagnetic responses emerging from the interplay of their electronic band topology and magnetism. We begin by introducing the fundamental topological properties of the electrons in Weyl semimetals, and provide an overview of the characteristic phenomena arising from their band topology, such as the anomalous Hall effect and chiral magnetic effect. The materials exhibiting the magnetic Weyl semimetal state, with ferromagnetic ordering, antiferromagnetic ordering, etc., are listed. The possible mechanisms for their magnetism are discussed in connection with the Weyl electrons. Non-uniform magnetic textures and magnetization dynamics are expected to exhibit a topological interplay with the Weyl electrons, manifesting as spinmotive force and spin torques. We also review the magnetotransport phenomena such as domain wall magnetoresistance, studied by mesoscopic scale calculations. Finally, we mention the spin transport properties studied in magnetic Weyl semimetals. The topological nature of Weyl electrons reviewed here is important not only for fundamental physics, but also for the potential application to low-dissipative electronics and spintronics devices.

cond-mat.mes-hall↗

arXiv2026

Emergence of Social Reality of Emotion through a Social Allostasis Model with Dynamic Interpretants

The theory of constructed emotion defines social reality as the community-level consensus on emotion concepts assigned to interoceptive sensations arising from bodily allostasis and social interaction. In this study, we simulate this emergence process using a computational model that integrates symbol emergence with degrees of freedom in symbol interpretation and active inference. Two agents receive interoceptive signals, exchange inferred symbols, and simultaneously adapt their bodily control goals and symbol interpretations to each other. Experimental results show that the interoceptive prior preferences and symbol probability distributions of the two agents converge, confirming the emergence of social reality grounded in social consensus.

cs.MA↗

arXiv2026

Phase-shift instanton approach to tunneling duality in Read--Rezayi state

We study the duality between quasi-particle and electron tunneling in point-contact geometries of fractional quantum Hall states. To treat non-Abelian edge operators, we introduce a "phase-shift instanton" that incorporates phase factors from primary fields into the instanton gas framework. Using this method, we reformulate the Moore--Read duality and obtain an explicit dual description for the $k=3$ Read-Rezayi state. Our results clarify how quasi-particle tunneling produces characteristic phase shifts in instantons and how these shifts map strong quasi-particle tunneling to weak electron tunneling. Based on this dual description, we analytically evaluate the non-linear differential conductance in the strong-coupling regime. We reveal that, due to the physical requirement that the tunneling particle across the vacuum gap must be a true fermion, the transport behavior universally converges to a $G \propto V^4$ scaling for both the Moore--Read and Read--Rezayi states. This universal transport signature highlights a fundamental topological constraint underlying non-Abelian fractional quantum Hall edges.

cond-mat.mes-hall↗

arXiv2026

Universal Transport Theory for Paired Fractional Quantum Hall States in the Quantum Point Contact Geometry

Even-denominator fractional quantum Hall (FQH) states can be viewed as topological superconductors of composite fermions, supporting a charged chiral mode and $|\mathcal{C}_{cf}|$ neutral Majorana modes set by the Chern number $\mathcal{C}_{cf}$. Despite ongoing efforts, distinguishing the many competing paired phases remains an open problem. In this work, we propose a unified theory of charge transport across a quantum point contact (QPC) for general paired FQH states described by an $so(N)_1 \times u(1)$ conformal field theory. We derive the boundary effective action for an arbitrary number of Majorana fermions $N=|\mathcal{C}_{cf}|$ and develop a non-perturbative instanton approximation to describe tunneling processes. We establish a weak-strong duality relating strong quasiparticle tunneling to weak electron tunneling. We calculate the scaling dimensions of the tunneling operators and demonstrate that while the weak-coupling fixed point is generally unstable, the strong-coupling fixed point is stable for physically relevant filling fractions and number of Majorana fermions. These transport exponents provide a distinct experimental fingerprint to identify the topological phases of even-denominator FQH states.

cond-mat.mes-hall↗

arXiv2026

Collective excitations in magnetic topological insulators and axion dark matter search

We investigate collective excitations in magnetic topological insulators (TIs) and their impact on axion detection. In the three-dimensional TI model with the Hubbard term, the effective action of magnons and amplitude modes is formulated by dynamical susceptibility under the antiferromagnetic and ferromagnetic states. One of the amplitude modes is identified as ``axionic'' quasi-particle and its effective coupling to the electromagnetic fields turns out to be roughly unchanged, or suppressed by up to two orders of magnitude, compared to the previous estimate, which may drastically change the sensitivity of the axion search using``axion' in magnetic TIs.

hep-ph↗

arXiv2026

Nonlinear spin-motive force driven by mixed-space quantum geometry

Spin-motive force, i.e., the electric current induced by magnetization dynamics, is theoretically studied beyond the Thouless-pump paradigm. In contrast to the linear-response regime, where the induced current is purely AC, we show that spin-motive force acquires both a DC component and a second-harmonic component at nonlinear order in magnetization dynamics. We further clarify that both contributions originate from the geometric properties of electronic bands -- quantum geometry defined in the mixed parameter space $({\boldsymbol k}, {\boldsymbol m})$ spanned by electron's momentum ${\boldsymbol k}$ and magnetization ${\boldsymbol m}$. By applying the theory to a Luttinger model, we demonstrate that our mechanism yields a finite nonlinear current even in the insulating regime, and the resulting electrical signal is measurable in a conventional current-measurement setup. Our findings offer a new operating principle of AC-to-DC conversion with magnetic materials, highlighting the pivotal role of the $({\boldsymbol k}, {\boldsymbol m})$-mixed space quantum geometry in magnetization-dynamics-induced electric currents.

cond-mat.mes-hall↗

arXiv2026

Topological superconductivity on a kagome magnet coupled to a Rashba superconductor

A quantum anomalous Hall system is predicted to realize topological superconductivity when proximity-coupled to an $s$-wave superconductor. A kagome magnet with chiral magnetic ordering exhibits the quantum anomalous Hall effect; however, superconducting proximity to an ordinary $s$-wave superconductor fails to induce pairing in the strong exchange coupling limit. In this work, we demonstrate that proximity coupling to a Rashba superconductor gives rise to topological superconducting phases characterized by odd Bogoliubov-de Gennes Chern numbers. We confirmed their consistency with the chiral central charge calculated based on the modular commutator. We also show that the magnetic ordering of kagome magnets is affected energetically by the proximity effect.

cond-mat.mes-hall↗

arXiv2025

Chirality-selective proximity effect between chiral $p$-wave superconductors and quantum Hall insulators

Heterostructures of superconductors and quantum-Hall insulators are promising platforms of topological quantum computation. However, these two systems are incompatible in some aspects such as a strong magnetic field, the Meissner effect, and chirality. In this work, we address the condition that the superconducting proximity effect works in the bulk of quantum Hall states, and identify an essential role played by the vortex lattice regardless of pairing symmetry. We extend this finding to a heterostructure of a chiral $p$-wave superconductor in the mixed state and an integer quantum Hall insulator. The proximity effect works selectively in the lowest Landau level depending on relative chiralities. If the chiralities align, a topological phase transition to a topological superconductor occurs.

cond-mat.mes-hall↗

arXiv2025

The First Star-by-star $N$-body/Hydrodynamics Simulation of Our Galaxy Coupling with a Surrogate Model

A major goal of computational astrophysics is to simulate the Milky Way Galaxy with sufficient resolution down to individual stars. However, the scaling fails due to some small-scale, short-timescale phenomena, such as supernova explosions. We have developed a novel integration scheme of $N$-body/hydrodynamics simulations working with machine learning. This approach bypasses the short timesteps caused by supernova explosions using a surrogate model, thereby improving scalability. With this method, we reached 300 billion particles using 148,900 nodes, equivalent to 7,147,200 CPU cores, breaking through the billion-particle barrier currently faced by state-of-the-art simulations. This resolution allows us to perform the first star-by-star galaxy simulation, which resolves individual stars in the Milky Way Galaxy. The performance scales over $10^4$ CPU cores, an upper limit in the current state-of-the-art simulations using both A64FX and X86-64 processors and NVIDIA CUDA GPUs.

astro-ph.GA↗

arXiv2025

Decentralized Collective World Model for Emergent Communication and Coordination

We propose a fully decentralized multi-agent world model that enables both symbol emergence for communication and coordinated behavior through temporal extension of collective predictive coding. Unlike previous research that focuses on either communication or coordination separately, our approach achieves both simultaneously. Our method integrates world models with communication channels, enabling agents to predict environmental dynamics, estimate states from partial observations, and share critical information through bidirectional message exchange with contrastive learning for message alignment. Using a two-agent trajectory drawing task, we demonstrate that our communication-based approach outperforms non-communicative models when agents have divergent perceptual capabilities, achieving the second-best coordination after centralized models. Importantly, our decentralized approach with constraints preventing direct access to other agents' internal states facilitates the emergence of more meaningful symbol systems that accurately reflect environmental states. These findings demonstrate the effectiveness of decentralized communication for supporting coordination while developing shared representations of the environment.

cs.MA↗

arXiv2025

Navigating Phase Transitions with Path-Finding Algorithms: A Strategic Approach to Replica Exchange Monte Carlo

The replica exchange method is a powerful tool for overcoming slow relaxation in molecular simulations, but its efficiency depends strongly on the choice of the number and interval of replicas and their exchange probabilities. Here, we propose a new optimization scheme based on the Dijkstra algorithm that constructs an optimal exchange path by representing replicas and their exchange probabilities as a graph. Inspired by path-finding techniques widely used in computer science, including applications in game algorithms, our approach ensures that transitions follow a minimum entropy gradient path and effectively speeds up sampling even in systems exhibiting slow relaxation near critical points or phase transition regions. The method provides a systematic way to improve replica exchange efficiency and offers new insights into the control of relaxation dynamics, as demonstrated through applications to the solid-liquid phase transition of the Lennard-Jones bulk system.

cond-mat.stat-mech↗

arXiv2025

Fermi arcs around magnetic domain walls in a compensated ferrimagnetic Weyl semimetal Ti$_2$MnAl

Fermi arcs are one of the characteristic features of Weyl semimetals, appearing as surface states that connect Weyl points with opposite chiralities. It has also been suggested that Fermi arcs can emerge in the bulk due to the interplay between magnetic textures and Weyl physics. We focus on Ti$_2$MnAl which is an ideal magnetic Weyl semimetal with a compensated ferrimagnetic order. We systematically analyze domain wall-induced Fermi arcs in Ti$_2$MnAl using an effective tight-binding model. By varying the strength of spin-orbit coupling, we confirmed that these domain wall-induced Fermi arcs emerge as a result of shifts in the positions of the Weyl points. Furthermore, we found that these domain wall-induced Fermi arcs in Ti$_2$MnAl originate from the Chern number and represent a topologically robust state that is independent of the domain wall width.

cond-mat.mes-hall↗

arXiv2024

Quantum anomalous, spin, and valley Hall effects in pentalayer rhombohedral graphene moiré superlattices

Recent experiments on pentalayer rhombohedral graphene moiré superlattices have observed the quantum anomalous Hall effect at moiré filling factor of $ν= 1$ and various fractional values. These phenomena are attributed to a flat Chern band induced by electron-electron interactions. In this study, we demonstrate that at $ν= 2$, many-body effects can lead to the emergence of quantum spin Hall and quantum valley Hall states, in addition to the quantum anomalous Hall state, even in the absence of spin-orbit coupling or valley-dependent potentials. These three topological states can be selectively induced by the application and manipulation of a magnetic field. Furthermore, we show that at $ν= 3$ and $4$, the ground state can be a combination of topologically trivial and nontrivial states, unlike the cases of $ν=1$ and 2. This contrasts with the conventional quantum Hall effect in graphene where the ground state at filling factor $ν$ is given as the particle-hole counterpart at $4-ν$.

cond-mat.str-el↗

arXiv2024

Topological Spin-Orbit Torque in Ferrimagnetic Weyl Semimetal

The spin-orbit torque (SOT) in a compensated ferrimagnetic Weyl semimetal, ${\rm Ti}_{2}{\rm MnAl}$, is studied by the linear response theory. We elucidate that the SOT driven by all the occupied electronic states is present in magnetic Weyl semimetal, unlike in conventional metallic magnets. Around the energy of the Weyl points, we find that such an SOT is dominant and almost independent of the disorder. The emergence of the SOT in ${\rm Ti}_{2}{\rm MnAl}$ can be understood from the structure of the mixed Berry curvature around the Weyl points, which is similar to that of the ordinary Berry curvature.

cond-mat.mes-hall↗

arXiv2024

Andreev-like Reflection in the Pfaffian Fractional Quantum Hall Effect

We studied the tunnel transport between the edge of a Pfaffian fractional quantum Hall state and that of an integer quantum Hall state. Based on the duality argument between the strong and weak tunnelings, we found that an Andreev-like reflection appeared in the strong tunneling regime. We calculated the charge conductance in the weak and strong tunneling regimes for the low-voltage limit. In the weak tunneling limit, $dI}/dV$ was proportional to $V^{1/ν}$ with bias voltage $V$ and $ν=1/2$. By contrast, in the strong tunneling limit, $dI/dV$ was expressed by $(e^{2}/h)2ν/(1+ν)$ with a correction term. We expect that this condition can be realized experimentally at the point contact between a fractional quantum Hall state with $ν=5/2$ and an integer quantum Hall state with $ν=3$.

cond-mat.mes-hall↗