Takatsugu Masuda Group
Group of Solid State Physics (The Institute for Solid State Physics) [Neutron Science]
Experience and enjoy a discovery by yourself.
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Masuda group studies novel quantum phenomena realized in low dimensional quantum spin system, oxygen molecule magnet, and multiferroics materials by combination of crystal growth, bulk property measurement, and neutron scattering. Any students who have interest in quantum phenomena, crystal growth, bulk property measurement, neutron scattering experiment, doing experiment abroad, presentation abroad at international symposium, etc., are very welcomed to our group.
Associate Professor Takatsugu Masuda
- 1996 Department of applied physics, Faculty of engi neering, University of Tokyo
- 1999 Research associate, Department of Advanced Materials Science, Graduate School of Frontier Science,
- 2002 Dr. Technology, Department of Applied Physics, University of Tokyo
- 2002 Postdoctoral research associate, Oak Ridge National Laboratory,
- 2005 Associate professor, Yokohama City University,
- 2010 Associate professor, University of Tokyo Hobby: Butterfly, Tennis, Mountaineering, Jogging
Introduction of the study
Here we will introduce two examples of our recent study, break down of quasiparticle in antiferromagnet and nematic correlation in frustrated magnet.
Many phenomena in condensed matter science can be explained by using the concept of quasiparticle. For example antiferromagnetic order is a result of Bose condensation of magnons and superfluidity is those of phonons. The quasiparticle, however, can be unstable and decay if allowed by conservation laws. It was initially predicted in superfluid Helium and was identified by a termination of the excitation at twice the energy of a roton. Recently the magnon version of the spectral termination was predicted in the 2D square lattice Heisenberg antiferromagnets (SLHAF) in high magnetic field. At zero field a two-magnon continuum spreads in the higher energy region for all wave vector q and there is no decay channel. With increasing field the one-magnon branch moves to higher energy around q = (π π) and eventually overlaps with the continuum at a threshold field. The hybridization of one-magnon with two-magnon continuum induces instability of the one-magnon. Our group experimentally observed the magnon instability in S=5/2 SLHAF Ba2MnGe2O7 by using neutron scattering technique.
One of the recent interests in condensed matter science is to search for a spin liquid that exhibits order not in a conventional two-spin correlation but in other correlations such as magnetic multipole or spin chirality. A 1D frustrated spin chain with a ferromagnetic nearest-neighbor interaction ( J1) and an antiferromagnetic next-nearest-neighbor interaction ( J2) is diversity of such novel states. In zero field vector spin chirality does order with a broken Z2 symmetry. At a field close to the ferromagnetic polarized phase, a pair of magnons form a bound state, and its Bose condensation at approximately q = π induces the quasi-long-range order of transverse spin nematic correlation 〈S+0 S+1 S?l S?l+1〉. At the same time longitudinal two spin correlation exhibits spin density wave like sinusoidal behavior. Our group explored such novel states in ferromagnetic frustrated chain LiCuVO4 and identified the SDW-like order in high magnetic field.
Message from a senior
Masuda sensei is sometimes strict but mostly gentle. In principle he respects students’ autonomy and we do our research by ourselves. In weekly meeting we make presentation on our progress of study and Masuda-sensei gives useful advice.