ISSP - The institute for Solid State Physics

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Tokunaga Group
Associate Professor

Research Associate

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Magnetic fields have been extensively used in broad research fields of solid state physics because they can directly tune the spins, orbitals and phases of electrons in materials. We study various kinds of phase transitions in high magnetic fields with using non-destructive pulse magnets and developing/up-grading various experimental techniques; e.g. magnetization, magnetoresistance, electric polarization, polarizing optical microscopy, and so on. As one of our recent projects, we focus on the electronic states in the quantum limit state. Since charge carriers are confined in the smallest cyclotron orbit, Coulomb interaction dominates over the kinetic energy. Therefore, we can realize strongly correlated electron systems in the quantum limit states. In particular, we have been focusing on the semimetals having even number of electrons and holes, and found a novel field-induced phase in graphite and anomalous quantum transport properties in black phosphorus under multiple extreme conditions. We are also studying multiferroic materials using high precision experiments realized in pulsed-fields. We found a field-induced novel multiferroic phase in a triangular lattice chiral antiferromagnet CsCuCl3 and bipolar resistive memory effects in a room temperature multiferroic material BiFeO3. 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.

Magnetoresistance of a single crystal of black phosphorus under multiple extreme conditions. Inset shows schematic illustration of the crystal structure. Resistance along the c axis was measured in magnetic fields applied along the a axis. We observed huge positive magnetoresistance larger than 1,000 times of the value at zero field together with superposed Shubnikov-de Haas oscillations.
(left) Schematic illustration of the arrangement of Cu ions in a chiral antiferromagnet CsCuCl3. (right) Field-induced changes of electric polarization along the a axis in applied magnetic fields along the b* axis.

Research Subjects

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