Many-body quantum phases in electron-hole system in semiconductors

Photo-excited electron-hole (e-h) system in semiconductors exhibits various phases depending on the e-h density and temperature, such as exciton gas, electron-hole plasma, and electron-hole liquid (droplets). Since the density of e-h pair can be easily controlled by changing the light intensity, the system provides an unique playground to study the phase transition dynamics in which many body Coulomb interaction plays an essential role. Theoretically, Bose Einstein condensation or e-h BCS state have been anticipated to exist at very low temperature. By using laser spectroscopy technique exemplified by terahertz spectroscopy, we are studying the dynamics of metal-insulator transition (exciton Mott transition) and liquid-gas transition in e-h system in the ultrafast temporal resolution of several picoseconds.

Formation dynamics of exciton in Si probed by broadband THz spectroscopy.
A development of excitons can be identified around  200 ps after
instantaneous optical excitation of
free e-h gas through the 1S-2P transition of exciton located at 12meV.

Ref.) T. Suzuki and R. Shimano, Phys. Rev. Lett. 103, 057401 (2009).
T. Suzuki and R. Shimano, Phys. Rev. B 83, 085207 (2011).
T. Suzuki and R. Shimano, Phys. Rev. Lett. 109, 046402 (2012).

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Shimano Laboratory Department of Physics, School of Science, The University of Tokyo