arXiv subjects

Takayuki Yokoyama

Publications and source records attributed to Takayuki Yokoyama.

4 recordsLinked to original sources

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 Néel phase. We then extend this framework to infinite cylinders of the spin-$1/2$ XY-$J_χ$ 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

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

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↗