arXiv subjects

Yasuhiro Tada

Publications and source records attributed to Yasuhiro Tada.

At least 19 recordsLinked to original sources

arXiv2026

Evidence for interior-gap pair-density-wave state in Kondo-Heisenberg chains

Interior-gap superconductivity has long been discussed as an exotic paired state in the presence of Fermi-surface mismatch, but its realization in canonical strongly correlated models has remained elusive. Here we present evidence that the superconducting phase of one-dimensional Kondo-Heisenberg models realizes an interior-gap pair-density-wave (PDW) state generated by strong correlations. Combining infinite density-matrix-renormalization-group (iDMRG) and finite DMRG calculations for $S=1/2$ and $S=3/2$ chains, we show that the PDW correlation is the dominant bulk superconducting correlation in the spin-gapped regime and that the momentum distribution function $n(k)$ exhibits a reconstructed structure characteristic of interior-gap physics. In particular, while the feature in $n(k)$ for the $S=1/2$ chain is only hump-like, the corresponding structure in the $S=3/2$ chain develops into a clear dip, strongly supporting the interpretation in terms of an interior-gap-like dip structure. Unlike conventional interior-gap scenarios based on a mismatch between preexisting Fermi surfaces, the present system starts from a single bare conduction-electron Fermi surface, and the additional low-energy single-particle structure emerges dynamically together with the dominant PDW correlation through the Kondo coupling. Finite DMRG data further demonstrate that boundary effects can substantially modify real-space correlations in this gapless one-dimensional system, making a direct thermodynamic-limit calculation essential for identifying the intrinsic bulk momentum structure and the dominant correlation channel.

cond-mat.str-el↗

arXiv2026

Artificial-gauge-field-driven reentrant charge-density-wave phase in a three-leg Bose-Hubbard ladder

We investigate hard-core bosons at half filling on a three-leg ladder under the uniform artificial gauge field. By analyzing current patterns and correlation functions, we uncover a rich quantum phase diagram containing multiple superfluid and insulating phases. In bosonic ladder systems, increasing the gauge flux typically destabilizes the Meissner phase and leads to vortex phases characterized by circulating currents. In the present system, however, we find that charge-density-wave (CDW) phases emerge precisely in such a flux regime despite the presence of only an on-site interaction, where vortex states are naturally expected and are indeed realized in nearby parameter regions. While part of this behavior can be qualitatively understood from a strong-coupling perspective, we also identify an isolated CDW region that cannot be connected to such limits. Furthermore, upon increasing the artificial gauge flux, we observe a reentrant sequence of quantum phase transitions, CDW $\to$ vortex-superfluid $\to$ CDW, revealing a strong competition between the vortex phase and the density-wave order.

cond-mat.quant-gas↗

arXiv2026

Diagnosing energy gap in quantum spin liquids via polarization amplitude

Identifying whether a many-body ground state is gapped or gapless is a fundamental yet challenging problem, especially in quantum spin liquids. In this work, we develop a gap-diagnostic scheme based on the polarization amplitude defined via a twist operator, evaluated within the infinite density-matrix renormalization group (iDMRG) framework. As a benchmark, analysis of the spin-$1/2$ XXZ chain demonstrates that the polarization amplitude clearly distinguishes the gapless Tomonaga-Luttinger liquid from the gapped N\'eel phase. We then extend this framework to infinite cylinders of the spin-$1/2$ XY-$J_\chi$ model on the square lattice. We find that the polarization amplitude sharply detects the transition between the gapless XY phase and the gapped chiral spin liquid phase. These results show that polarization amplitudes provide a strong energy-gap diagnostic in two-dimensional frustrated quantum magnets, including quantum spin liquids.

cond-mat.str-el↗

arXiv2025

Spin susceptibility in quasicrystal superconductor with spin-orbit interactions

We study impacts of spin-orbit interactions on the spin susceptibility in quasicrystal superconductors, motivated by the anomolous superconducting properties in the van der Waals quasicrystal Ta$_{1.6}$Te under magnetic fields. We consider the Penrose tiling model with $s$-wave pairing as a representative system and include anisotropic spin-orbit interactions allowed for the quasicrystal structure. It is shown that the spin-momentum locking locally takes place in the quasicrystal, and electron motion and spin directions are tightly connected at each spatial position in the real space. As a result, the spin susceptibility is enhanced for both in-plane and out-of-plane magnetic fields in the presence of a Rashba-type spin-orbit interaction. For an Ising-type spin-orbit interaction, the spin susceptibility only for in-plane magnetic fields is increased, while the out-of-plane spin susceptibility is almost unchanged. When there are both kinds of the spin-orbit interactions, temperature dependence of the spin susceptibility for any field directions is suppressed.

cond-mat.supr-con↗

arXiv2025

Strain-induced quantum oscillation in Kitaev spin liquid with Majorana-Fermi surface

We theoretically study Landau quantization of itinerant Majorana quasiparticles induced by lattice strain in a Kitaev spin liquid with Majorana Fermi surfaces. We consider the isotropic spin-1/2 Kitaev model on the honeycomb lattice with a perturbation such as a staggered Zeeman field and an electromagnetic field, which generates small Majorana Fermi surfaces near the Dirac points. By introducing triaxial strain, we create an effective vector potential that couples to Majorana fermions and leads to Landau quantization. Our calculations show that the low-energy spectrum forms discrete pseudo-Landau levels of the Majorana Fermi surface. We further demonstrate that the strain-induced effective vector potential gives rise to pronounced quantum oscillations of the density of states and the specific heat at very low temperatures, in close analogy to the de Haas-van Alphen effect for charged electrons in metals. These results indicate that Landau-quantization-driven "Majorana quantum oscillations" can serve as a probe of the charge-neutral Majorana Fermi surface in Kitaev materials.

cond-mat.str-el↗

arXiv2025

Polarization-based indices in quantum many-body systems: validity and extension beyond one dimension

The expectation value of the twist operator has been widely used as a polarization-based index for gapped and gapless phases in interacting quantum many-body systems. Although numerous studies support this usage in specific settings and rigorous results have established the validity of the criterion in important settings, the precise assumptions required for it to sharply distinguish gapped and gapless phases under more general conditions have not been fully clarified. In this work, we clarify the logical status of polarization-based indices by formulating symmetry-based statements under explicitly stated assumptions. We identify the role of ground-state degeneracy in the statements for gapped systems and clarify the distinct assumptions required to exclude gapless scenarios that could otherwise mimic gapped behavior in the thermodynamic limit. Building on this controlled framework, we construct a meaningful extension beyond one dimension, emphasizing that such an extension is nontrivial and cannot be obtained by a straightforward generalization of the one-dimensional twist operator. Our results delineate the regime in which polarization-based quantities are justified as sharply defined many-body indices.

cond-mat.str-el↗

arXiv2025

Projectification of point group symmetries with a background flux and Lieb-Schultz-Mattis theorem

We discuss the Lieb-Schultz-Mattis (LSM) theorem in two-dimensional spin systems with on-site ${\mathrm U}(1)\rtimes {\mathbb Z}_2$ spin rotation symmetry and point group $C_{2v}$ symmetry about a site. We ``twist" the point group symmetry by introducing a small uniform U(1) flux to obtain a projective symmetry, similarly to the familiar magnetic translation symmetry. The LSM theorem is proved in presence of the flux and then it is demonstrated that the theorem holds also for the flux-free system. Besides, the uniform flux enables us to show the LSM theorem for the time-reversal symmetry and the site-centered $C_2$-rotation symmetry.

cond-mat.str-el↗

arXiv2025

Stability of quasi-particle creation and multiband geometry in fractional Chern insulators under magnetic fields

We study creation of quasi-particles in fractional Chern insulators (FCI) under magnetic fields. We consider two representative models, the Kapit-Mueller model and the checkerboard model, which have distinct band properties in terms of the quantum geometry. The former satisfies the so-called ideal condition and well mimics the lowest Landau level, while the latter is not ideal for realization of FCI states. It is found within exact diagonalization that both quasi-holes and quasi-electrons are stably created by the magnetic fields in the Kapit-Mueller model. On the other hand, stability of the quasi-particle creation depends on directions of the magnetic field in the checkerboard model. Although the quasi-electron creation is stable under a magnetic field, the quasi-hole creation and the underlying FCI state are unstable for the opposite field direction, leading to a field-induced non-FCI state. We point out that this difference can be understood based on the multiband quantum geometry in the presence of the magnetic fields.

cond-mat.str-el↗

arXiv2025

Spin nematic order and superconductivity in $J_1$-$J_2$ Kondo lattice model on square lattice

We investigate competition and cooperation of magnetic frustration and the Kondo effect in the $J_1$-$J_2$ Kondo lattice model on the square lattice at zero temperature. In this model, the frustrated interactions $J_1,J_2$ between the localized spins stabilize spin nematic orders, while the Kondo coupling favors local spin singlets. Using the slave boson mean field approximation, we find that the spin nematic order remains stable against small Kondo coupling, and the localized spins and the conduction electrons are effectively decoupled. On the other hand, a standard Fermi liquid state is formed for sufficiently strong Kondo interactions. Furthermore, in an intermediate region with moderate Kondo coupling, the spin nematic order and the Kondo effect coexist, and superconducting pairing of the conduction electrons is induced by the spinon pairing. We discuss the ground state phase diagram and nature of the quantum phase transitions between the different superconducting states.

cond-mat.str-el↗

arXiv2024

Anomalous enhancement of Neel order in the $S = 1/2$ square lattice Heisenberg model under fictitious magnetic field

Fictitious magnetic fields can be introduced in quantum magnets by the strain engineering and the Aharonov-Casher effect. Here, we study impacts of a uniform fictitious magnetic field and corresponding Landau quantization on the Neel order in the $S=1/2$ Heisenberg model on the square lattice as a prototypical system of quantum magnets. We first analyze the system by using the spin-wave approximation. It is found that the staggered magnetization is enhanced by the fictitious magnetic field and it shows a simple scaling behavior with respect to the magnetic length, in contrast to a naive expectation based on the Dzyaloshinskii-Moriya interaction. We also perform density matrix renormalization group calculations to fully take quantum effects into account and obtain quantitatively more accurate results. The enhancement is found to be anomalously strong and it shows a non-trivial scaling behavior or a fluctuation induced discontinuity. These results are beyond the well known understanding of correlated systems under magnetic fields called the magnetic catalysis.

cond-mat.str-el↗

arXiv2024

Quantized polarization in a generalized Rice-Mele model at arbitrary filling

We discuss the charge polarization in a generalized Rice-Mele model at arbitrary particle filling per site as a model of charge ordered systems in one dimension. The model possesses neither the conventional bond-centered inversion symmetry nor the one site translation symmetry alone, but has combinations of these symmetries. We show that the charge polarization in the ground state is quantized by the combined symmetry and is characterized solely by the filling. Especially, the polarization can be $1/2$ (mod 1) in the zero filling limit. Under the open boundary condition, there exist excess charges accumulated near edges of the system irrespective of existence or absence of edge modes. Correspondingly, we decompose the polarization into a bulk contribution and an edge contribution, and numerically demonstrate that the polarization is dominated by the former (latter) when the energy gap is large (small). We also discuss a simple generalization of our model and examine absence/existence of a gapless edge mode protected by the inversion symmetry by introducing intra unit cell and inter unit cell contributions of the charge polarization.

cond-mat.str-el↗

arXiv2024

Impurity effects in one dimensional spin nematic liquid

We study impurity effects in the spin nematic phase of the $S=1/2$ $J_1$-$J_2$ frustrated spin chain under an external magnetic field by using the infinite density matrix renormalization group and the bosonization. It is found that local magnetization almost saturates around the impurity and the entanglement entropy nearly vanishes at the corresponding bonds, not only when the magnetic interactions near the impurity are weakened but also when they are strengthened compared to those in the bulk. Then, we examine spin correlations and Friedel oscillations induced by the impurity. The bosonization provides a qualitative understanding of the characteristic behaviors of the magnetization. We also discuss impacts of the impurity on experiments by focusing on NMR spectra.

cond-mat.str-el↗

arXiv2023

Many-body multipole index and bulk-boundary correspondence

We propose new dipole and quadrupole indices for interacting insulators with point group symmetries. The proposed indices are defined in terms of many-body quantum multipole operators combined with the generator of the point group symmetry. Unlike the original multipole operators, these combined operators commute with Hamiltonian under the symmetry and therefore their eigenvalues are quantized. This enables a clear identification of nontrivial multipolar states. We calculate the multipole indices in representative models and show their effectiveness as order parameters. Furthermore, we demonstrate a bulk-boundary correspondence: a non-zero index implies the existence of edge/corner states under the the point group symmetry.

cond-mat.str-el↗

arXiv2022

Gapless symmetry-protected topological phase of quantum antiferromagnets on anisotropic triangular strip

We study a three-leg spin-1/2 ladder with geometrically frustrated interleg interactions. We call this model an anisotropic triangular-strip (ATS) model. We numerically and field-theoretically show that its ground state belongs to a gapless symmetry-protected topological (SPT) phase. The numerical approach is based on density-matrix renormalization group analyses of the entanglement entropy and the entanglement spectrum. Whereas the entanglement entropy exhibits a critical behavior, the entanglement spectrum is nontrivially degenerate. These entanglement properties imply that the ground state is a gapless topological phase. We investigate the ATS model using a quantum field theory to support the numerical findings. When the frustrated interchain interaction is deemed a perturbation acting on the three spin chains, the frustrated interchain interaction almost isolates the second chain from the other two chains. However, at the same time, the second chain mediates a ferromagnetic interaction between the first and third chains. Therefore, the ground state of the ATS model is a gapless Tomonaga-Luttinger liquid weakly coupled to a spin-1 Haldane chain with irrelevant interactions. Last but not least, we show that the gapless SPT phase of the ATS model is a symmetry-protected critical phase. We point out that the symmetry protection of criticality is essential in characterization of the gapless SPT phase.

cond-mat.str-el↗

arXiv2021

Revisiting Anderson-Higgs mechanism: application of Lieb-Schultz-Mattis theorem

We consider an electron model of superconductivity on a three-dimensional lattice where there are on-site attractive Hubbard interaction and long-range repulsive Coulomb interaction. It is claimed that fully gapped $s$-wave superconductivity within this model, if present, exhibits spontaneous translation symmetry breaking possibly related to a charge order. Our discussions are based on an application of the Lieb-Schultz-Mattis theorem under some physical assumptions. The inconsistency between the proposed supersolid and experiments can impose some constraints on a reasonable choice of a theoretical model.

cond-mat.supr-con↗

arXiv2021

Lieb-Schultz-Mattis theorem in higher dimensions from approximate magnetic translation symmetry

We prove the Lieb-Schultz-Mattis (LSM) theorem on the energy spectrum of a general two or three-dimensional quantum many-body system with the U(1) particle number conservation and translation symmetry. Especially, it is demonstrated that the theorem holds in a system with long-range interactions. To this end, we introduce approximate magnetic translation symmetry under the total magnetic flux $\Phi=2\pi$ instead of the exact translation symmetry, and explicitly construct low energy variational states. The energy spectrum at $\Phi=2\pi$ is shown to agree with that at $\Phi=0$ in the thermodynamic limit, which concludes the LSM theorem.

cond-mat.str-el↗

arXiv2021

Robust orbital diamagnetism of correlated Dirac fermions in chiral Ising universality class

We study orbital diamagnetism at zero temperature in $(2+1)$-dimensional Dirac fermions with a short-range interaction which exhibits a quantum phase transition to a charge density wave (CDW) phase. We introduce orbital magnetic fields into spinless Dirac fermions on the $\pi$-flux square lattice, and analyze them by using infinite density matrix renormalization group. It is found that the diamagnetism remains intact in the Dirac semimetal regime as a result of a non-trivial competition between the enhanced Fermi velocity and magnetic-field-induced mass gap, while it is monotonically suppressed in the CDW regime. Around the quantum critical point (QCP) of the CDW phase transition, we find a scaling behavior of the diamagnetism characteristic of the chiral Ising universality class. This defines a universal behavior of orbital diamagnetism in correlated Dirac fermions around a QCP, and therefore the robust diamagnetism in the semimetal regime is a universal property of Dirac systems whose criticality belongs to the chiral Ising universality class. The scaling behavior may also be regarded as a quantum, magnetic analogue of the critical Casimir effect which has been widely studied for classical phase transitions.

cond-mat.str-el↗

arXiv2020

Quantum criticality of magnetic catalysis in two-dimensional correlated Dirac fermions

We study quantum criticality of the magnetic field induced charge density wave (CDW) order in correlated spinless Dirac fermions on the $\pi$-flux square lattice at zero temperature as a prototypical example of the magnetic catalysis, by using the infinite density matrix renormalization group. It is found that the CDW order parameter $M(B)$ exhibits an anomalous magnetic field $(B)$ scaling behavior characteristic of the $(2+1)$-dimensional chiral Ising universality class near the quantum critical point, which leads to a strong enhancement of $M(B)$ compared with a mean field result. We also establish a global phase diagram in the interaction-magnetic field plane for the fermionic quantum criticality.

cond-mat.str-el↗