arXiv subjects

Y. Otaki

Publications and source records attributed to Y. Otaki.

2 recordsLinked to original sources

arXiv2019

Higher-order topological insulators in a magnetic field

Two-dimensional (2D) generalization of the Su-Schriffer-Heeger (SSH) model serves as a platform for exploring higher-order topological insulators (HOTI). We investigate this model in a magnetic field which interpolates two models studied so far with zero flux and $π$ flux per plaquette. We show that in the Hofstadter butterfly there appears a wide gap around the $π$ flux, which belongs to the same HOTI discovered by Benalcazar-Bernevig-Hughes (BBH). It turns out that in a weak field regime HOTI could exist even within a small gap disconnected from the wider gap around $π$ flux. To characterize HOTI, we employ the entanglement polarization (eP) technique which is useful even if the basic four bands split into many Landau levels under a magnetic field.

cond-mat.mes-hall↗

arXiv2019

Edge states, corner states, and flat bands in a two-dimensional $\cal PT$ symmetric system

We study corner states on a flat band in the square lattice. To this end, we introduce a two dimensional model including Su-Schrieffer-Heeger type bond alternation responsible for corner states as well as next-nearest neighbor hoppings yielding flat bands. The key symmetry of the model for corner states is space-time inversion ($\cal PT$) symmetry, which guarantees quantized Berry phases. This implies that edge states as well as corner states would show up if boundaries are introduced to the system. We also argue that an infinitesimal $\cal PT$ symmetry-breaking perturbation could drive flat bands into flat Chern bands.

cond-mat.mes-hall↗