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Tsunetsugu Group

Research Associate

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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 high-harmonic generation (HHG) in solids illuminated by laser. We have formulated this by Floquet theory and showed a different scaling behavior with the input frequency compared with more traditional HHG using gases.

High-harmonic spectrum of electron current in a one-dimensional tight-binding model of electrons. The cutoff order Nmax represented by the arrow is proportional to FΩ–1EΩ–2 in contrast to the conventional scaling Nmax ∝ Ω–1 in atomic gases, where E and Ω are amplitude and frequency of input electric field, respectively, and FEΩ–1 is the electron-light coupling.

Research Subjects

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