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Masuda Group
Associate Professor

Research Associate

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One of the research goals in our group is to find a novel quantum phenomenon and to reveal its mechanism in low-dimensional spin magnets and frustrated magnets. Strong quantum fluctuation or geometrical frustration disturbs the development of trivial magnetic states and induces a non-trivial quantum state. Furthermore such a state is sensitive to a small perturbation and, thus, the area is frontier of quantum phenomena. Our research topic includes spin liquid, RVB, Cuboc structure, etc. Another goal is to observe a new magnetoelectric effect in multiferroic compounds and/or relaxor magnets. Figures show the experiment and calculation of the pressure variations of the spin dynamics in the frustrated quantum magnet CsFeCl3. In the disordered phase at low pressures single mode of singlet – doublet excitation is observed. In contrast in the pressured induced ordered phase at 1.4 GPa, it was discovered that the hybridized mode of longitudinal and transverse fluctuations originated from noncollinearity of the magnetic structure as well as Nambu-Goldstone and Higgs-amplitude modes.

Spin dynamics of the frustrated quantum magnet CsFeCl3 under pressure. The panels (a) – (c) show inelastic neutron spectra. The color plots are the data measured by a chopper spectrometer HRC in J-PARC, and the symbols are those measured by a triple axis spectrometer CTAX in research reactor HFIR in Oak Ridge National Laboratory. In the spectra at P = 0.0 GPa (a) and P = 0.3 GPa (b) in the disordered phase, singlet-triplet excitations are observed. In contrast in the one at P = 1.4 GPa (c) in the pressure induced ordered phase, magnon excitations are observed. The panels (d) – (f) show the calculated result by extended spin wave theory. At P = 1.4 GPa (f) the hybridized mode of transverse and longitudinal fluctuations (h-TL) does exist in addition to Nambu-Goldstone (NG) and Higgs-amplitude (L) modes. The h-TL mode is ascribed to the noncollinearity of the magnetic structure, and it is observed in the neutron spectrum in the panel (c).

Research Subjects

  1. Nontrivial excitation mode in frustrated magnet near quantum critical point
  2. Detection of spin wave spin current by neutron
  3. Local control of spin moment in multiferroics
  4. Search of spin liquid
  5. Observation of field induced nonreciprocal magnon