285 citations · 1.3k across the 15 of their papers we have counts for
15 papers
Non-Hermitian skin effect enforced by nonsymmorphic symmetries
Yutaro Tanaka, Ryo Takahashi, Ryo Okugawa
Crystal symmetries play an essential role in band structures of non-Hermitian Hamiltonian. In this paper, we propose a non-Hermitian skin effect (NHSE) enforced by nonsymmorphic sy…
Discriminant indicators with generalized inversion symmetry
Tsuneya Yoshida, Ryo Okugawa, Yasuhiro Hatsugai
We propose indicators of the discriminant for systems with generalized inversion symmetry which are computed from data only at high-symmetry points in the Brillouin zone. Our appro…
Rotoinversion-symmetric bulk-hinge correspondence and its applications to higher-order Weyl semimetals
Yutaro Tanaka, Ryo Takahashi, Ryo Okugawa +1
We give a bulk-hinge correspondence for higher-order topological phases protected by rotoinversion symmetry in magnetic systems. Our approach allows us to show t…
Mirror-symmetry-protected dynamical quantum phase transitions in topological crystalline insulators
Ryo Okugawa, Hiroki Oshiyama, Masayuki Ohzeki
Dynamical quantum phase transitions (DQPTs) are topologically characterized in quantum quench dynamics in topological systems. In this paper, we study Loschmidt amplitudes and DQPT…
Non-Hermitian band topology with generalized inversion symmetry
Ryo Okugawa, Ryo Takahashi, Kazuki Yokomizo
Non-Hermitian skin effects and exceptional points are topological phenomena characterized by integer winding numbers. In this study, we give methods to theoretically detect skin ef…
Second-order topological non-Hermitian skin effects
Ryo Okugawa, Ryo Takahashi, Kazuki Yokomizo
Higher-order topology realizes topologically robust corner modes as a manifestation of nontriviality. We theoretically propose non-Hermitian skin effects which stem from second-ord…
Topological exceptional surfaces in non-Hermitian systems with parity-time and parity-particle-hole symmetries
Ryo Okugawa, Takehito Yokoyama
We study a topological band degeneracy in non-Hermitian systems with parity-time () and parity-particle-hole () symmetries. In -dimensional non-Hermitian systems, it is…
Generic phase diagram for Weyl superconductivity in mirror-symmetric superconductors
Ryo Okugawa, Takehito Yokoyama
We study topological phase transitions in three-dimensional odd-parity or noncentrosymmetric superconductors with mirror symmetry when time-reversal symmetry is broken. We construc…
Topological semimetals studied by ab initio calculations
Motoaki Hirayama, Ryo Okugawa, Shuichi Murakami
In topological semimetals such as Weyl, Dirac, and nodal-line semimetals, the band gap closes at points or along lines in k space which are not necessarily located at high-symmetry…
Universal phase transition and band structures for spinless nodal-line and Weyl semimetals
Ryo Okugawa, Shuichi Murakami
We study a general phase transition between spinless topological nodal-line semimetal and Weyl semimetal phases. We classify topological nodal lines into two types based on their p…
Emergence of topological semimetals in gap closing in semiconductors without inversion symmetry
Shuichi Murakami, Motoaki Hirayama, Ryo Okugawa +1
A band gap for electronic states in crystals governs various properties of solids, such as transport, optical and magnetic properties. Its estimation and control have been an impor…
Topological Dirac Nodal Lines and Surface Charges in fcc Alkaline Earth Metals
Motoaki Hirayama, Ryo Okugawa, Takashi Miyake +1
In nodal-line semimetals, the gaps close along loops in space, which are not at high-symmetry points. Typical mechanisms for the emergence of nodal lines involve mirror s…
In-plane electric polarization of bilayer graphene nanoribbons by interlayer bias voltage
Ryo Okugawa, Junya Tanaka, Takashi Koretsune +2
We theoretically show that an interlayer bias voltage in the AB-stacked bilayer graphene nanoribbons with armchair edges induces an electric polarization along the ribbon. Both tig…
Weyl Node and Spin Texture in Trigonal Tellurium and Selenium
Motoaki Hirayama, Ryo Okugawa, Shoji Ishibashi +2
We study Weyl nodes in materials with broken inversion symmetry. We find based on first-principles calculations that trigonal Te and Se have multiple Weyl nodes near the Fermi leve…
Dispersion of Fermi arcs in Weyl semimetals and their evolutions to Dirac cones
Ryo Okugawa, Shuichi Murakami
We study dispersions of Fermi arcs in the Weyl semimetal phase by constructing a simple effective model. We calculate how the surface Fermi-arc dispersions for the top- and bottom…