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Osada Group

Research Associate TAEN, Toshihiro

Research Subjects

  • Topological properties of organic Dirac fermion systems
  • Electronic structure and quantum transport in two-dimensional materials
  • Angle-dependent magnetotransport and interlayer coherence in layered conductors
  • Quantum size effect of ultra-thinning on magnetic-field-induced electronic phase transitions in graphite

Osada group aims to search, elucidate, and control novel electronic states, quantum transport phenomena, and topological phenomena in atomic layer (two-dimensional) materials, topological materials, and artificial nanostructures, by transport measurements (dc/ac electric transport, thermoelectric effects, etc.) under high magnetic field, low temperature, and high pressure environments. The main experimental tools include device fabrication of atomic layers, their complex stacks and nanostructures using advanced microfabrication/evaluation equipment (electron-beam lithography etc.), precision measurement of double-axial angle dependence in superconducting magnets, high magnetic field measurement with 40T-class miniature pulse magnet. Simple theoretical studies are also performed in parallel. Recently, we have focused on topological electronic states (quantum Hall ferromagnetic state, Chern insulator state, etc.) and transport phenomena (nonlinear anomalous Hall effect, etc.) in organic Dirac fermion systems and τ-type organic conductors, quantum transport in twisted bilayer graphene and black phosphorus ultrathin films, and quantum size effect of ultra-thinning on the magnetic-field-induced electronic phase transitions in graphite.

(a) Band structure of organic Dirac fermion system with a charge order gap and Berry curvature of its conduction band. When the system carries electric current, the occupied region shifts from the Fermi surface. (b) Nonlinear anomalous Hall effect. (c) Chemical potential dependence of the Berry curvature dipole.
(a) Band structure of the nanoribbon of the τ-type organic conductor with a finite spin-orbit coupling. There appear helical edge states in the gap. (b) Energy levels of the τ-type organic conductor under magnetic fields. Spin splitting with orbital origin can been seen.

Publications and Research Highlights