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  • Letter

Terahertz emission spectroscopy of ultrafast exciton shift current in the noncentrosymmetric semiconductor CdS

M. Sotome1,*, M. Nakamura1,2, T. Morimoto2,3, Y. Zhang4, G.-Y. Guo1,5,6, M. Kawasaki1,3, N. Nagaosa1,3, Y. Tokura1,3,7, and N. Ogawa1,2,3

  • 1RIKEN Center for Emergent Matter Science (CEMS), Wako, 351–0198, Japan
  • 2PRESTO, Japan Science and Technology Agency (JST), Kawaguchi 332–0012, Japan
  • 3Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Tokyo, 113–8656, Japan
  • 4Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
  • 5Department of Physics, National Taiwan University, Taipei 10617, Taiwan
  • 6Physics Division, National Center for Theoretical Sciences, Taipei 10617, Taiwan
  • 7Tokyo College, University of Tokyo, Tokyo 113–8656, Japan

  • *Author to whom correspondence should be addressed: masato.sotome@riken.jp
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Phys. Rev. B 103, L241111 – Published 21 June, 2021

DOI: https://doi.org/10.1103/PhysRevB.103.L241111

Abstract

The charge-neutral exciton has been predicted to carry genuine photocurrent due to the geometric Berry phase of the electronic bands, if the inversion symmetry in a crystal is broken. We detect such exciton shift current in a prototypical polar semiconductor CdS by using terahertz emission spectroscopy. A distinct peak emerges in the photocurrent spectra at the energy of the exciton resonance, which is demonstrated to result from the distinct displacements of electrons and holes in real space within the excitons to produce a finite transient charge current at subpicosecond time scale. Our findings elucidate the Berry phase physics of the charge-neutral photoexcitations and also shed light on the novel energy harvesting mechanism by exciton generation.

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Phys. Rev. B 103, L241111– Published 21 June, 2021
  • Received 14 May 2020
  • Revised 5 May 2021
  • Accepted 25 May 2021
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