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

Letter

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

M. Sotome, M. Nakamura, T. Morimoto, Y. Zhang, G.-Y. Guo, M. Kawasaki, N. Nagaosa, Y. Tokura, and N. Ogawa

Phys. Rev. B 103, L241111 – Published 21 June 2021

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.

Received 14 May 2020
Revised 5 May 2021
Accepted 25 May 2021

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

Physics Subject Headings (PhySH)

Excitons Photovoltaic effect Ultrafast optics

Solar cells

First-principles calculations Terahertz techniques

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

M. Sotome^1,*, M. Nakamura^1,2, T. Morimoto^2,3, Y. Zhang ⁴, G.-Y. Guo^1,5,6, M. Kawasaki^1,3, N. Nagaosa^1,3, Y. Tokura^1,3,7, and N. Ogawa^1,2,3

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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Issue

Vol. 103, Iss. 24 — 15 June 2021

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