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Kondo Group

Research Associate MORI, Ryo

Research Subjects

  • Development of a laser-excited ARPES system with ultra-high energy resolution
  • Superconductivity and topological quantum phase investigated by angle-, spin-, and time-resolved photoemission spectroscopy
  • Strongly correlated physics studied by photoemission with synchrotron radiation

The momentum-resolved band structure provides fundamental information to understand the electronic properties of materials. The angle-resolved photoemission spectroscopy (ARPES) is a powerful technique to visualize the band structure by mapping the intensities of photoelectrons as a function of angle and energy. With the spin-resolved technique, we can also identify the spin-polarized character of the band. In addition, the time-resolved ARPES realized with a pump-probe technique can track the reordering process of electron system from its nonequilibrium state. In our laboratory, we utilize these various ARPES techniques and study the following phenomena: nonconventional superconductors, heavy fermions, strongly correlated systems, topological quantum phases, and quantum well states. Furthermore, we develop a new ARPES machine capable of achieving both the lowest measurement temperature and the highest energy resolution in the world by innovating a 3He cryostat and a laser source. The state-of-art equipment will enable us to identify even a subtle electronic feature close to the Fermi level, such as an energy gap and a mode-coupled dispersion, which is typically tied to exotic behaviors of conduction electrons.

(a)Crystal structure of Bi2Sr2CuO6+d high-Tc superconductor. (b) ARPES analyzer. (c) Diagram of ARPES experiment. (d) Snapshot of dispersion image. (e) Whole band structure. (f) Competition between superconducting gap and pseudogap. (g) Spectra around Fermi surface below (red) and above (black) superconducting transition temperature (Tc = 35K). (h) Difference between the curves in (g). (h) Coherent spectral weight is painted with a red color, which is corresponding to the red region represented in (f).

Publications and Research Highlights