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

Authors
  • SIM, SANGWAN
  • LEE, SEUNGMIN
  • MOON, JISOO
  • IN, CHIHUN
  • LEE, JEKWAN
  • NOH, MINJI
  • KIM, JEHYUN
  • JANG, WOOSUN
  • CHA, SOONYOUNG
  • SEO, SEUNGYOUNG
  • OH, SANGSHIK
  • KIM, DOHUN
  • SOON, ALOYSIUS
  • JO, MOON HO
  • CHOI, HYUNYONG
Publication Date
Mar 18, 2020
Source
[email protected]
Keywords
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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 bulkinsulating 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. / 1 / N

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