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

Title
Picosecond Competing Dynamics of Apparent Semiconducting-Metallic Phase Transition in the Topological Insulator Bi2Se3
Authors
SIM, SANGWANLEE, SEUNGMINMOON, JISOOIN, CHIHUNLEE, JEKWANNOH, MINJIKIM, JEHYUNJANG, WOOSUNCHA, SOONYOUNGSEO, SEUNGYOUNGOH, SANGSHIKKIM, DOHUNSOON, ALOYSIUSJO, MOON HOCHOI, HYUNYONG
Date Issued
Mar-2020
Publisher
American Chemical Society
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.
URI
http://oasis.postech.ac.kr/handle/2014.oak/101852
ISSN
2330-4022
Article Type
Article
Citation
ACS Photonics, vol. 7, no. 3, page. 759 - 764, 2020-03
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 JO, MOON HO
Dept of Materials Science & Enginrg
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