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Takeyama Group

Research Associate

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We are engaged in development for generating ultra-high magnetic fields above 100 T, and pursue the solid-state science realized under such an extreme condition. We employ two methods for the ultra-high magnetic field generation, one is the electro-magnetic flux compression (EMFC) and the other is the single-turn coil (STC) method. We have established a new type of coil for the EMFC, and currently the maximum magnetic field is 730 T. This value is the highest achieved thus far in an indoor setting in the world. Further development is underway for achieving much higher fields, more precise and reliable measurements for the solid-state physics. We are now involved in construction of ultra-high magnetic field generator system under the 1000 T project. The horizontal and vertical (H- and V-) STCs are used for more precise measurements up to 300 T, respectively, in accordance with their magnetic field axes. The H-STC is mainly used for magneto-optical measurements by use of laser optics, whilst the V-STC is more suitable for the study of low-temperature magnetization in a cryogenic bath. We are conducting the studies on magneto-optics of carbon nano-materials or of semiconductor nano-structures as well as on the critical magnetic fields in superconducting materials and on the high-field magnetization processes of the magnetic materials with highly frustrated quantum spin systems.

Newly-developed ultra-high magnetic field generator of the electro-magnetic flux compression method. The 5MJ fast condenser bank is capable of supplying maximum electrical current of amount to 8 mega-ampere, which is injected to a primary coil through the collector plate. By upgrading the performance such as the maximum charging voltage and the residual impedance, ultra-high magnetic fields up to 1000 T are planned to generate.
The exciton Aharonov-Bohm(A-B) splitting in semiconducting carbon nanotubes (CNT) was observed by streak spectroscopic measurements in ultra-high magnetic fields above 300 T. Upon applying a very intense magnetic field along an axis of a semiconducting single-walled CNT, the band-edge exciton absorption spectrum shows up as a splitting as a result of A-B magnetic flux. A magnetic field of 367 T, generated by the electromagnetic flux compression destructing pulsed magnet-coil technique, was applied to single-chirality semiconducting CNTs. Using streak spectroscopy, we demonstrated separation of the independent band-edge bright exciton states at the K and K’ points of the Brillouin zone after the mixing of the dark and bright states above 100 T. These results enable a quantitative discussion of the whole picture of the A-B effect in single-walled CNTs.

Research Subjects

  1. Technical developments for ultra-high magnetic field magnets above 100 T and for solid-state physics measurements
  2. Magneto-optics in ultra-high magnetic fields
  3. Magnetization processes of magnetic materials and the critical magnetic field in superconducting materials in ultra-high magnetic fields