arXiv subjects

Satoshi Okamoto

Publications and source records attributed to Satoshi Okamoto.

At least 19 recordsLinked to original sources

arXiv2026

Quantum Wake Dynamics from Distinct Spectroscopic Perturbations

Quantum wake dynamics in quantum magnets have recently been inferred from the dynamical spin structure factor, which probes only a restricted class of local perturbations. Here, we show that resonant inelastic x-ray scattering (RIXS) selection rules act as an operator filter on fractionalized excitations, producing distinct quantum wakes in the spin-$\frac{1}{2}$ Heisenberg antiferromagnetic chain. Using explicit real-time evolution of single-spin and spin-conserving bond correlators, we find that the conventional spin response propagates up to the maximum spinon velocity, $v_s=\frac{\pi}{2} J$, whereas the bond channels concentrate their spectral weight into a slower dominant wake with $v\simeq 0.92 J$, while weaker components remain bounded by the full spinon light cone. The corresponding momentum- and frequency-resolved responses map onto experimentally accessible RIXS channels, demonstrating that different spectroscopic perturbations resolve complementary pathways of many-body propagation beyond the neutron-scattering spin structure factor. Their inelastic spectral weights further provide access to quantum Fisher information, while equal-time bond sum rules connect the same spectroscopic channels to the ground-state energy. Because the same correlators can be prepared and measured on quantum hardware, they also define direct, experimentally anchored benchmarks for quantum simulations, particularly in frustrated and higher-dimensional magnets where controlled classical real-time calculations become challenging.

cond-mat.stat-mech↗

arXiv2026

Electronic manipulation of polar order in electron crystal

When interaction among atoms or ions is strong enough, they often arrange periodically, forming a crystal. The arrangement patterns of atoms or ions can encode information, a concept that has enabled devices such as ferroelectric memories. It has been found that not only atoms or ions but also electrons in condensed matter can crystallize when Coulomb interaction is strong enough. Typical examples are charge-ordered states in solids, where different valences, or different electron numbers, of an ion spontaneously form a spatial pattern on the lattice. In such electron crystals, information is expected to be encoded into the electron-ordering patterns. Here, we demonstrate electronic manipulation and readout of charge-ordering directions in a paramagnetic semiconductor LuFe$_2$O$_4$. By applying current pulses at room temperature, we observed that the non-reciprocal resistivity of LuFe$_2$O$_4$ is modulated along with a sign reversal, which disappears above the charge-ordering temperature. A numerical calculation incorporating inter-band Berry curvature affected by the charge ordering is consistent with the experimental results. By applying the observed phenomenon, we also demonstrate a non-reciprocal resistance memory operation in the charge-ordered LuFe$_2$O$_4$. This result opens the door to realizing charge-ordering electronics.

cond-mat.mtrl-sci↗

arXiv2026

Electrically Programmable Correlated Topology and Magnetism in a Moir\'e Trilayer

Strong electron-electron interactions underlie a wide range of quantum many-body phenomena, including magnetism, superconductivity, and charge fractionalization. A central goal is to achieve in situ control over lattice geometry, bandwidth, and band topology within a single platform. Here we realize such an electrically programmable quantum many-body system in an alternating twisted trilayer MoTe$_2$, where an out-of-plane displacement field continuously modifies the layer polarization, effective lattice, and topology of the moir\'e bands. At zero displacement field, the system realizes a triangular lattice hosting a correlated insulator at one hole per moir\'e unit cell ($\nu = -1$). Doping this state produces strongly asymmetric magnetic responses: double-exchange-like ferromagnetism for $|\nu| > 1$, and signatures of spin polarons and antiferromagnetism for $|\nu| < 1$. At large displacement field, interlayer hybridization reconstructs the electronic structure into a honeycomb lattice with a flat Chern band, supporting integer and fractional Chern insulators. Magneto-optical measurements further reveal the signatures of gap closure and Landau-level formation from a spin-polarized Fermi surface near the crossover between the two regimes. These results establish a unified, electrically tunable platform in which correlated magnetism and topological states emerge from a single controllable band structure.

cond-mat.mes-hall↗

arXiv2026

Berry curvature and field-induced intrinsic anomalous Hall effect in an antiferromagnet FeTe

Berry curvature is ubiquitous in condensed matter physics and materials science. Its main consequence is the intrinsic anomalous Hall effect (AHE) in magnetic materials and plays a pivotal role in spintronic applications and quantum technologies. Here, we present a theoretical study of the intrinsic AHE in tetragonal FeTe, a semimetallic van der Waals antiferromagnet with compensated magnetic ordering at low temperatures. Using a realistic spin-fermion model, we demonstrate that FeTe exhibits a large Berry-curvature-driven AHE under an applied magnetic field. Our calculations reveal that the Hall conductivity of this compound is extremely sensitive to temperature and field strength and even exhibits sign reversal, highlighting FeTe as a prototypical platform where magnetism and topology combine to produce robust intrinsic Hall responses. This work establishes FeTe as a promising candidate for exploring quantum transport in low-dimensional correlated systems. We also discuss the implications for recent experimental results of the AHE and ordinary Hall effect reported for FeTe.

cond-mat.mtrl-sci↗

arXiv2026

Intrinsic Topological Weyl Phase Transition Induced by a Magnetostructural Transformation in a Kagome Magnet

Topological phase transitions provide a unique window into the interplay between structure, magnetism, and Weyl physics in magnetic Weyl semimetals. However, realizing an intrinsic Weyl phase transition between two distinct Weyl states near room temperature remains challenging. Here, we demonstrate that a magnetostructural transition effectively induces such a transition in the kagome magnet Mn$_3$Ga. High-resolution neutron diffraction, magnetization characterizations and first-principles calculations reveal that Mn$_3$Ga undergoes a chiral antiferromagnetic transition below 485 K, followed by a magnetostructural transition to a monoclinic structure with highly canted antiferromagnetic order near room temperature. These cooperative changes in lattice and magnetic symmetries reorganize Weyl nodes, driving a transition from a primary type-II Weyl state to a distinct Weyl state, accompanied by dramatic variations in the anomalous Hall effect and appearance of topological Hall effect. Our findings open a new pathway for discovering novel topological Weyl states and potential spintronic applications.

cond-mat.str-el↗

arXiv2026

Kinetic obstruction to pairing in the doped Kitaev-Heisenberg ladder

We investigate the hole-doped Kitaev-Heisenberg ($t$-$J$-$K$) model on a two-leg ladder geometry using the density-matrix renormalization group (DMRG). We first consider the behavior of the antiferromagnetic Kitaev (AFK) spin-liquid phase as a function of hopping strength $t$ and doping level. This reveals intriguing pairing tendencies only for $\frac{t}{K} \lesssim 0.65$, consistent with prior results on three-leg ladders, and firmly supports the emerging picture that the physics of doped Kitaev spin liquids strongly depends on the kinetic energy of the doped holes. Analysis of one- and two-hole doping uncovers close links between the spatial profiles of the plaquette operator and the charge density. We construct a doping-dependent phase diagram for antiferromagnetic Heisenberg interactions and intermediate hopping $t=1$. Upon doping, the rung-singlet region develops dominant superconducting correlations. Charge-density-wave correlations dominate at weak doping near the transition to the stripy phase. Spin-density wave-like behavior is found in the AFK and ferromagnetic Kitaev limits, and in the stripy phase.

cond-mat.str-el↗

arXiv2025

Compressive Strain Turns $s^{\pm}$ into $d$-Wave Pairing in One-unit-cell La$_3$Ni$_2$O$_7$ Thin Film Via Substrate-Induced Hole Doping

Motivated by recent reports of ambient-pressure superconductivity in La$_3$Ni$_2$O$_7$ films grown on LaSrAlO$_4$, we investigate the superconducting instability in a one-unit cell thin film using {\it ab initio} and random-phase approximation techniques. Compared to the high-pressure bulk system, the ratio of inter-layer $d_{3z^2-r^2}$ hopping to intra-layer $d_{x^2-y^2}$ hopping is suppressed in the 1UC thin film, and the crystal-field splitting of the $e_g$ orbitals is increased. Our calculation indicates that spin-fluctuation-driven pairing correlations are weak for the stoichiometric case at ambient pressure, but increase significantly under hole doping. The leading pairing symmetry is also found to change by hole doping. Specifically, we obtain a leading $d_{x^2-y^2}$ pairing state at moderate hole doping, followed by a $d_{xy}$ state at higher doping. These states are driven by intra-band spin-fluctuation scattering {\it within} the $\gamma$ hole pocket centered around the M point, and arise primarily from states in the Ni layer {\it farther} from the substrate. These results strongly suggest that the thin-film superconducting samples are hole-doped and that pairing in this system predominantly arises in the layer, as opposed to the inter-layer pairing in the pressurized bulk system.

cond-mat.supr-con↗

arXiv2025

Simulation of Topological $X$-Gates via Braiding of Majorana Zero Modes in an Interacting Quantum Dot System

Recent advances in quantum dot platforms have opened new pathways for realizing Majorana zero modes (MZMs) and simulating topological quantum computation. Here we propose an experimentally feasible setup for implementing topological $\sqrt{X}$- and $X$-quantum gates in an interacting $Y$-shaped quantum-dot array. The proposed novel architecture enables both braiding and charge readout through simple fusion operations controlled by gate-tunable potentials. Using many-body time-dependent simulations based on exact diagonalization, we analyze the braiding and fusion dynamics of MZMs in the presence of nearest-neighbor Coulomb interactions and pairing disorder. We compute diabatic errors, braiding fidelity, and the time- and space-resolved electron and hole components of the local density of states to monitor the braiding process. Our results show that even weak interactions or pairing disorder induce oscillations in the braiding fidelity, thereby setting an upper bound on the braiding speed. Furthermore, we demonstrate that comparing fusion outcomes before and after braiding provides a direct and experimentally accessible signature of the non-Abelian nature of MZMs in quantum dot systems.

cond-mat.str-el↗

arXiv2025

Isolated spin ladders in Ln$_2$Ti$_9$Sb$_{11}$ (Ln:La-Nd) metals

Here we present the discovery and characterization of a series of antimonides Ln$_2$Ti$_9$Sb$_{11}$ (Ln: La--Nd) which exhibit well-isolated, $n=2$ rare-earth spin ladders. We discuss the structure of the new compounds, with a particular focus on the magnetic Ln spin ladders. Nd$_2$Ti$_9$Sb$_{11}$ and Ce$_2$Ti$_9$Sb$_{11}$ exhibit antiferromagnetic interactions and a well-defined doublet ground state, whereas Pr$_2$Ti$_9$Sb$_{11}$ exhibits a weakly magnetic singlet ground state. Nd$_2$Ti$_9$Sb$_{11}$ is a poor metal with an electrical resistivity of 0.1m$\Omega$-cm at 300K and weak temperature dependence. The thermal conductivity along the ladder exhibits significant field dependence even at 40K, considerably higher than the magnetic ordering temperature of 1.1K. Compared to compounds with transition metal spin ladders, the rare-earth elements impart much lower energy scales, making these compounds highly tunable with external stimuli like magnetic fields. The diverse magnetism of the rare-earth ions and RKKY interactions further contribute to the potential for a wide array of rich magnetic ground states, positioning these materials as a rare example of an inorganic square spin-ladder platform.

cond-mat.str-el↗

arXiv2025

Unveiling In-Gap States and Majorana Zero Modes in Superconductor-Topological Insulator Bilayer model

Interfaces between topological insulators and superconductors are promising platforms for realizing Majorana zero modes (MZMs) via the superconducting proximity effect. We introduce a bilayer model consisting of the surface states of a three-dimensional topological insulator (3DTI) coupled to an $s$-wave superconductor and systematically study the role of interlayer tunneling strength ($t_\perp$). We find that increasing $t_\perp$ shifts the proximity-induced (PrI) gap minima away from the $\Gamma$-point, giving rise to momentum-selective interference patterns that manifest as spatial oscillations in the in-gap states. By introducing an antidot with a magnetic vortex in the SC layer, we investigate the nature of in-gap states including MZMs and Caroli-de Gennes-Matricon (CdGM) modes. With increasing hybridization strength, the energy separation between MZMs and CdGM states increases, enhancing the isolation of MZMs. Importantly, in the strong hybridization limit, the leading CdGM separation remains large inspite of the decrease in the PrI gap. Spin- and spatial-resolved wavefunction analysis reveals angular momentum asymmetries absent in conventional $s$-wave systems. A direct comparison with a standalone $s$-wave superconductor confirms the emergence of distinct $p$-wave-like features in the bilayer geometry. Our results provide experimentally relevant predictions for tuning the stability of MZMs and their differentiation from the CdGM modes in SC-3DTI heterostructures and offer a theoretical framework for probing unconventional superconductivity in engineered topological systems.

cond-mat.supr-con↗

arXiv2025

General trends of electronic structures, superconducting pairing, and magnetic correlations in the Ruddlesden-Popper nickelate $m$-layered superconductors La$_{m+1}$Ni$_{m}$O$_{3m+1}$

We report a comprehensive theoretical analysis of the Ruddlesden-Popper layered nickelates La$_{m+1}$Ni$_m$O$_{3m+1}$ ($m = 1$ to 6) under pressure. Our results suggest that, while these Ruddlesden-Popper layered nickelates display many similarities, they also show noticeable differences. The Ni $d_{3z^2-r^2}$ orbitals display bonding-antibonding, or bonding-antibonding-nonbonding, characteristic splittings, depending on the even or odd number of stacking layers $m$. In addition, the ratio of the in-plane interorbital hopping between $d_{3z^2-r^2}$ and $d_{x^2-y^2}$ orbitals and in-plane intraorbital hopping between $d_{x^2-y^2}$ orbitals was found to be large in La$_{m+1}$Ni$_m$O$_{3m+1}$ ($m = 1$ to 6), and this ratio increases from $m = 1$ to $m = 6$, suggesting that the in-plane hybridization will increase as the layer number $m$ increases. In contrast to the dominant $s^\pm$--wave state driven by spin fluctuations in the bilayer La$_3$Ni$_2$O$_7$ and trilayer La$_4$Ni$_3$O$_{10}$, two nearly degenerate $d_{x^2-y^2}$-wave and $s^\pm$-wave leading states were obtained in the four-layer stacking La$_5$Ni$_4$O$_{13}$ and five-layer stacking La$_6$Ni$_5$O$_{16}$. The leading $s^\pm$-wave state was recovered in the six-layer material La$_7$Ni$_6$O$_{19}$. In general, at the level of the random phase approximation treatment, the superconducting transition temperature $T_c$ decreases in stoichiometric bulk systems from the bilayer La$_3$Ni$_2$O$_7$ to the six-layer La$_7$Ni$_6$O$_{19}$, despite the $m$ dependent dominant pairing. Both in-plane and out-of-plane magnetic correlations are found to be quite complex. Within the in-plane direction, we obtained the peak of the magnetic susceptibility at ${\bf q} = (0.6 \pi, 0.6 \pi)$ for La$_5$Ni$_4$O$_{13}$ and La$_7$Ni$_6$O$_{19}$, and at ${\bf q} = (0.7 \pi, 0.7 \pi)$ for La$_6$Ni$_5$O$_{16}$.

cond-mat.supr-con↗

arXiv2025

Novel phenomena in transition-metal oxide thin films and heterostructures with strong correlations and spin-orbit coupling

Transition-metal oxides have been a central subject of condensed matter physics for decades. In addition to novel electronic states driven by the influence of strong correlation, relativistic spin-orbit coupling effects have recently attracted much attention for their potential to explore topological phenomena. In this article, we review various experimental and theoretical studies on transition-metal oxides with focus on thin films and heterostructures where their physics is much influenced by correlation effects and spin-orbit coupling. The combination of the heterostructure geometry together with correlation and topology leads to a variety of novel states here reviewed. We also discuss perspectives for future research in this broad promising area.

cond-mat.mtrl-sci↗

arXiv2025

Electronic Structure, Magnetic and Pairing Tendencies of Alternating Single-layer Bilayer Stacking Nickelate La$_5$Ni$_3$O$_{11}$ Under Pressure

Nickelates have continued to surprise since their unconventional superconductivity was discovered. Recently, the layered nickelate La$_5$Ni$_3$O$_{11}$ with hybrid single-layer and bilayer stacking showed superconductivity under high pressure. This compound combines features of La$_2$NiO$_4$ and La$_3$Ni$_2$O$_7$, but its pairing mechanism remains to be understood. Motivated by this finding, here we report a comprehensive theoretical study of this system. Our density functional theory calculations reveal that the undistorted P4/mmm phase without pressure is unstable due to three distortion modes. Increasing pressure suppresses these modes and causes ``charge transfer'' between the single-layer and bilayer sublattices, leading to hole-doping in the single-layer blocks. Our random-phase approximation calculations indicate a leading $d_{x^2-y^2}$-wave pairing state that arises from spin-fluctuation scattering between Fermi surface states mainly originating from the single-layer blocks and additional weaker contributions from the bilayer blocks. These spin-fluctuations could be detected by inelastic neutron scattering as a strong peak at ${\bf q}=(\pi, \pi)$. Our findings distinguish La$_5$Ni$_3$O$_{11}$ from other nickelate superconductors discovered so far and the high-$T_c$ cuprates. We also discuss both similarities and differences between La$_5$Ni$_3$O$_{11}$ and other hybrid stacking nickelates.

cond-mat.supr-con↗

arXiv2025

Magnetic Permeability Time-varying Metamaterials at Microwave Frequencies

We demonstrate magnetic permeability time-varying metamaterials at GHz frequencies using ferromagnetic permalloy (Ni80Fe20; Py). We observe frequency up and down conversion of 4 GHz microwaves through the metamaterials, which is caused by the temporal modulation of permeability in the Py layer. Moreover, the efficiency of the up-conversion to a higher frequency is much larger than that of the down conversion to a lower frequency. These experimental results are reproduced well via numerical calculation, verifying that the significant up-conversion efficiency is traced back to nonlinear magnetization dynamics in the metamaterials. The present study opens a door to microwave sources toward the 6th-generation mobile communication system, four-dimensional metamaterials with spatio-temporal modulation, and nonlinear spintronics.

physics.optics↗

arXiv2025

Diabatic error and propagation of Majorana zero modes in interacting quantum dots systems

Motivated by recent experimental progress in realizing Majorana zero modes (MZMs) using quantum dot systems, we investigate the diabatic errors associated with the movement of those MZMs. The movement is achieved by tuning time-dependent gate potentials applied to individual quantum dots, effectively creating a moving potential wall. To probe the optimized movement of MZMs, we calculate the experimentally accessible local density-of-states and time-dependent fidelity using many-body time-dependent numerical methods. Our analysis reveals that an optimal potential wall height is crucial to preserve the well-localized nature of the MZM during its movement. Moreover, for the first time, we analyze diabatic errors in realistic quantum-dot systems, incorporating the effects of repulsive Coulomb interactions and disorder in both hopping and pairing terms. Additionally, we provide a comparative study of diabatic errors arising from the simultaneous versus sequential tuning of multiple gates during the MZMs movement. Finally, we estimate the time scale required for MZM transfer in a six-quantum-dot system, demonstrating that MZM movement is feasible and can be completed well within the qubit's operational lifetime in practical quantum-dot setups.

cond-mat.mes-hall↗

arXiv2024

Pairing tendencies in the doped Kitaev-Heisenberg model

We study the impact of hole-doping on the Kitaev-Heisenberg model on the honeycomb lattice. We investigate the pairing tendencies and correlation functions in the framework of a $t-J-K$ model using density matrix renormalization group calculations on three-leg cylinders. In the case of the pure Kitaev model, which realizes a quantum spin-liquid phase at half-filling, we find that binding of two holes only occurs at low values of the hopping, where the holes are slow. We have theoretically verified that pair formation occurs in the limit of immobile holes, where the pure Kitaev model remains exactly solvable. When we instead fix the hopping at an intermediate, more realistic, value, and vary the Heisenberg and Kitaev interaction strengths, we find pairing tendencies only in the N\'eel phase. This is in contrast to prior mean-field calculations, highlighting the importance of accounting for the kinetic energy of dopants in generalized Kitaev models. Interestingly, we also find signatures of pair-density wave formation over the studied range of model parameters, namely a periodic modulation of the charge density as well as the spin-spin and pair-pair correlations in real space. Moreover, we present a comparative study of the different correlations as a function of doping. We finally discuss the potential for experimentally observing the studied physics in quantum materials and heterostructures.

cond-mat.str-el↗

arXiv2024

MnRhBi3: A Cleavable Antiferromagnetic Metal

Cleavable metallic antiferromagnets may be of use for low-dissipation spintronic devices; however, few are currently known. Here we present orthorhombic MnRhBi3 as one such compound and present a thorough study of its physical properties. Exfoliation is demonstrated experimentally, and the cleavage energy and electronic structure are examined by density functional theory calculations. It is concluded that MnRhBi3 is a van der Waals layered material that cleaves easily between neighboring Bi layers, and that the Bi atoms have lone pairs extending into the van der Waals gaps. A series of four phase transitions are observed below room temperature, and neutron diffraction shows that at least two of the transitions involve the formation of antiferromagnetic order. Anomalous thermal expansion points to a crystallographic phase transition and/or strong magnetoelastic coupling. This work reveals a complex phase evolution in MnRhBi3 and establishes this cleavable antiferromagnetic metal as an interesting material for studying the interplay of structure, magnetism, and transport in the bulk and ultrathin limits as well as the role of lone pair electrons in interface chemistry and proximity effects in van der Waals heterostructures.

cond-mat.mtrl-sci↗

arXiv2024

In-plane Antiferromagnetism in Ferromagnetic Kagome Semimetal Co3Sn2S2

Co3Sn2S2 has been reported to be a Weyl semimetal with broken time-reversal symmetry with c axis ferromagnetism (FM) below a Curie temperature of 177 K. Despite the large interest in Co3Sn2S2, the magnetic structure is still under debate and recent studies have challenged our understanding of the magnetic phase diagram of Co3Sn2S2 by reporting unusual magnetic phases including the presence of exchange bias. Understanding the magnetism of Co3Sn2S2 is important since its electronic band structure including the much-celebrated flat bands and Weyl nodes depend on the magnetic phase. In this work, using X-ray Magnetic Circular Dichroism (XMCD), we establish that the magnetic moment in Co arises from the spin, with negligible orbital moment. In addition, we detect an in-plane AFM minority phase in the sea of a FM phase using spatially-resolved angle-resolved photoemission spectroscopy ({\mu}-ARPES) combined with density functional theory (DFT) calculation. Separately, we detect a sharp flat band precisely at the Fermi level (EF) at some regions in the sample, which we attribute to a surface state. The AFM phase survives even to the low temperature of 6 K. This example of entirely different magnetic ground states in a stoichiometric intermetallic invites further efforts to explore the observed AFM phase and understand the origin and nature of the magnetic and electronic inhomogeneity on the mesoscale and the interface between the AFM and FM phases.

cond-mat.mtrl-sci↗