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Tokunaga Group

member
Associate Professor TOKUNAGA, Masashi
Research Associate MIYAKE, Atsushi
Project Research Associate KINOSHITA, Yuto
Research Associate MITAMURA, Hiroyuki

Research Subjects

  • Field-induced transitions in multiferroic materials
  • Electronic phase transitions in the quantum limit state
  • High-speed polarizing microscope imaging in pulsed-high magnetic fields
  • High-field study of topological materials

Magnetic fields have been widely used in the research of solid-state physics as they can directly and continuously tune the spins, orbitals, and phases of electrons in materials. We explore novel quantum phenomena and non-trivial field effects in pulsed-high magnetic fields up to 60 T using various state-of-the-art experimental techniques to study their magnetic, transport, dielectric, structural, optical, and caloric properties. In BiFeO3, which is perhaps the most extensively studied multiferroic material, our high-field studies clarified microscopic origin of the magnetoelectric coupling and revealed non-volatile memory effect, magnetic control of ferroelastic strain, and a novel multiferroic phase at around room temperature. In addition, our high-field experiments on semimetals and semiconductors revealed novel insulating phase in graphite, valley polarization in bismuth, and quantum oscillations in semiconducting tellurium. In addition to these in-house studies, we accept about 40 joint research projects per year and study various localized/itinerant magnets and topological materials in high magnetic fields.

Field-angle dependence of magneto-electric effects in BiFeO3. The inset schematically shows rotation of the ferromagnetic moment and spin-driven electric polarization in the canted-antiferromagnetic states above 20 T.
Quantum oscillations observed in Hall resistance of a single crystal of Te. (inset) Field-angle dependence of differential peaks in Hall resistance shows two-dimensional behavior shown by the solid lines. This coincidence indicates existence of metallic surface states in semiconducting Te.

Publications and Research Highlights