ISSP - The institute for Solid State Physics

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Tsunetsugu Group
Professor
TSUNETSUGU,
Hirokazu

Research Associate
IKEDA,
Tatsuhiko

Research Associate
FUJII,
Tatsuya

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Strongly correlated electron systems, particularly compounds including d- or f-orbital electrons, are the main subjects of our research. In these systems where electron-electron interactions are very strong, a variety of interesting phenomena emerge at low temperatures, and various magnetic orders, unconventional superconductivity and density waves are typical cases. Targets of our recent study include novel types of quantum order and quantum fluctuations in frustrated spin and strongly correlated electronic systems with multiple degrees of freedom. In these systems, many soft modes of fluctuations are coupled, and this affects the nature of quantum phase transitions, as well as electronic states and dynamical properties including transport phenomena. One of our recent achievements is about a frustrated quantum spin system with spatially modulated exchange couplings. We have found that emergent multimer orders depend on the spin quantum number, and a tetramer order is stabilized in the S=3/2 case corresponding to some Cr compounds.

Quantum spins on the breathing pyrochlore lattice. Long and short bonds have exchange couplings J’ ≪ J.
Nearest-neighbor spin correlations inside units for the case of S = 3/2. Tetramer correlations are dominant. Antiferromagnetic and ferromagnetic correlations are shown by red and blue bonds, respectively and bond thickness schematically represents |SiSj|. Dashed lines show weak antiferromagnetic correlations between neighboring units.

Research Subjects

  1. Electronic states of strongly correlated systems with d- or f-electrons
  2. Statistical physics of frustrated systems
  3. Theory of novel phases in quantum magnets
  4. Unconventional superconductivity in strongly correlated electron systems