Picosecond Competing Dynamics of Apparent Semiconducting-Metallic Phase Transition in the Topological Insulator Bi2Se3

Sangwan Sim, Seungmin Lee, Jisoo Moon, Chihun In, Jekwan Lee, Minji Noh, Jehyun Kim, Woosun Jang, Soonyoung Cha, Seung Young Seo, Seongshik Oh, Dohun Kim, Aloysius Soon, Moon Ho Jo, Hyunyong Choi

Research output: Contribution to journalArticle

Abstract

Resolving the complex interplay between surface and bulk response is a long-standing issue in the topological insulators (TIs). Some studies have reported surface-dominated metallic responses, yet others show semiconducting-like bulk photoconductance. Using ultrafast terahertz spectroscopy with the advent of Fermi-level engineered TIs, we discovered that such difference arises from the time-dependent competing process of two parameters, namely, the Dirac-carrier surface scattering rate and the bulk Drude weight. After infrared femtosecond pulse excitation, we observed a metal-like photoconductance reduction for the prototypical n-type Bi2Se3 and a semiconductor-like increased photoconductance for the p-type Bi2Se3. Surprisingly, the bulk-insulating Bi2Se3, which is presumably similar to graphene, exhibits a semiconducting-to-metallic phase apparent transition at 10 ps. The sign-reversed, yet long-lasting (≥500 ps) metallic photoconductance was observed only in the bulk-insulating Bi2Se3, indicating that such dynamic phase transition is governed by the time-dependent competing interplay between the surface scattering rate and the bulk Drude weight. Our observations illustrate new photophysical phenomena of the photoexcited-phase transition in TIs and demonstrate entirely distinct dynamics compared to graphene and conventional gapped semiconductors.

Original languageEnglish
Pages (from-to)759-764
Number of pages6
JournalACS Photonics
Volume7
Issue number3
DOIs
Publication statusPublished - 2020 Mar 18

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Biotechnology
  • Atomic and Molecular Physics, and Optics
  • Electrical and Electronic Engineering

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    Sim, S., Lee, S., Moon, J., In, C., Lee, J., Noh, M., Kim, J., Jang, W., Cha, S., Seo, S. Y., Oh, S., Kim, D., Soon, A., Jo, M. H., & Choi, H. (2020). Picosecond Competing Dynamics of Apparent Semiconducting-Metallic Phase Transition in the Topological Insulator Bi2Se3 ACS Photonics, 7(3), 759-764. https://doi.org/10.1021/acsphotonics.9b01603