Strongly enhanced shift current at exciton resonances in a noncentrosymmetric wide-gap semiconductor

Masao Nakamura (), Yang-Hao Chan, Takahiro Yasunami, Yi-Shiuan Huang, Guang-Yu Guo, Yajian Hu, Naoki Ogawa, Yiling Chiew, Xiuzhen Yu, Takahiro Morimoto, Naoto Nagaosa, Yoshinori Tokura and Masashi Kawasaki
Additional contact information
Masao Nakamura: RIKEN Center for Emergent Matter Science (CEMS)
Yang-Hao Chan: Academia Sinica
Takahiro Yasunami: Bunkyo-ku
Yi-Shiuan Huang: National Taiwan University
Guang-Yu Guo: National Center for Theoretical Sciences
Yajian Hu: RIKEN Center for Emergent Matter Science (CEMS)
Naoki Ogawa: RIKEN Center for Emergent Matter Science (CEMS)
Yiling Chiew: RIKEN Center for Emergent Matter Science (CEMS)
Xiuzhen Yu: RIKEN Center for Emergent Matter Science (CEMS)
Takahiro Morimoto: Bunkyo-ku
Naoto Nagaosa: RIKEN Center for Emergent Matter Science (CEMS)
Yoshinori Tokura: RIKEN Center for Emergent Matter Science (CEMS)
Masashi Kawasaki: RIKEN Center for Emergent Matter Science (CEMS)

Nature Communications, 2024, vol. 15, issue 1, 1-9

Abstract: Abstract Excitons are fundamental quasiparticles that are ubiquitous in photoexcited semiconductors and insulators. Despite causing a sharp and strong photoabsorption near the interband absorption edge, charge-neutral excitons do not yield photocurrent in conventional photovoltaic processes unless dissociated into free charge carriers. Here, we experimentally demonstrate that excitons can directly contribute to photocurrent generation through a nonlinear light−matter interaction in a noncentrosymmetric semiconductor CuI. Epitaxial thin films of CuI exhibit a substantial enhancement of photocurrent at exciton resonance energies even below the bandgap. From the light polarization dependence, this photocurrent is identified to be shift current, a nonlinear photocurrent driven by the change in the geometric Berry phase of electron wave functions upon the optical transition. The shift current at the exciton resonance is much larger than that induced above the band gap by free electron−hole excitation, and their signs are opposite. First-principles calculations elucidate that the sign and magnitude of the exciton shift current are strongly dependent on the strain in the thin film. The present study reveals the crucial role of excitons in enhancing the shift current magnitude and its strain sensitivity, and will open an unprecedented route for efficient manipulation of nonlinear optical effects.

Date: 2024
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DOI: 10.1038/s41467-024-53541-6

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