Photoexcited carriers in three-dimensional topological insulators (3D TIs) decay rapidly through the electron-electron and electron-phonon scattering. While most studies focus on such fast dynamics, recent experiments find the slow photovoltage (PV) dynamics arising from the band-bending potentials, in which the optical transitions in two-dimensional electron gas (2DEG) are effective. Although early investigations speculated the existence of multiple band-bending structures from the TI surface to the TI bulk, how PV and 2DEG are correlated in the presence of such multiple band bendings has been less explored. Here, we employ the combination of time- and angle-resolved photoemission spectroscopy (tr-ARPES) and ultrafast time-resolved terahertz (tr-THz) spectroscopy to investigate the PV and 2DEG dynamics in the prototypical topological insulator Bi2Te3. Our tr-ARPES analysis identifies two spatially separated PV dynamics associated with two types of band bending: one is the well-known surface PV, and another PV is formed deep within the bulk, which we call "internal bulk PV."For the surface PV, our tr-THz spectra substantiate that the μs-long transient signal arises from the surface-PV-induced increase of the TSS and 2DEG carrier density, which appears as a transient blueshift of a Fermi cutoff and an increased ARPES intensity in the tr-ARPES measurements. In contrast, the effect of the internal bulk PV shows only marginal changes in the 2DEG and TSS carrier densities but shifts the entire binding energy of the near-surface bands.
|Journal||Physical Review B|
|Publication status||Published - 2022 Nov 15|
Bibliographical noteFunding Information:
B.L., S.K., I.K., M.-C.L., and T.W.N. were supported by the Institute for Basic Science (IBS) in Korea (Grant No. IBS-R009-D1). S.K. was supported by the Global Ph.D. Fellowship Program (Grant No. NRF-2015H1A2A1034943). Y.I. was supported by KAKENHI (Grants No. 17K18749, No. 18H01148, and No. 19KK0350). S.S. was supported by KAKENHI (Grant No. 19H00651) Y.I. acknowledges the sabbatical stay in IBS-CCES financially supported by the University of Tokyo. Y.I. is a Young Scientist Fellow of IBS-CCES. J.K. and J.H.K. were supported by the National Research Foundation of Korea (NRF) (Grants No. 2021R1A2C3004989 and No. 2017R1A5A1014862, vdWMRC SRC Program). J.K., N.H.J., and M.-H.J. were supported by the National Research Foundation of Korea (NRF) (Grant No. 2020R1A2C3008044). K.K. was supported by the National Research Foundation of Korea (NRF) (Grants No. 2020R1A2C3013454 and No. 2020R1A4A1019566). H.C. was supported by the National Research Foundation of Korea (NRF) through the government of Korea (MSIT) (Grants No. 2018R1A2A1A05079060, No. 2019R1A6A1A10073437, No. NRF-2021R1A2C3005905, and No. NRF-2020M3F3A2A03082472, Creative Materials Discovery Program (Grant No. 2017M3D1A1040828), Scalable Quantum Computer Technology Platform Center (Grant No. 2019R1A5A1027055)), the Ministry of Education of Korea (Core Center Program (Grant No. 2021R1A6C101B418)), and the Institute for Basic Science (IBS), Korea, under Project Code No. IBS-R014-G1-2018-A1. Part of this study has been performed using facilities at IBS Center for Correlated Electron Systems, Seoul National University.
© 2022 American Physical Society.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics