Time-Resolved Second-Harmonic Generation in Topological Insulator Bi2Te3: Competing Contributions from Dirac Surface States, Surface Photovoltage, and Band Bending

Sinha, A and Mithun, KP and Sood, AK (2023) Time-Resolved Second-Harmonic Generation in Topological Insulator Bi2Te3: Competing Contributions from Dirac Surface States, Surface Photovoltage, and Band Bending. In: ACS Photonics .

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Abstract

Nonlinear optical experiments, especially the second-harmonic generation (SHG) of topological insulators (TIs) such as Bi2Te3 and Bi2Se3, provide significant insights into the second-order nonlinear susceptibility (�(2)) of the topological surface states (TSS) and the DC electric field (Edc), formed by the intrinsic band bending between the surface and bulk states. Importantly, by selectively tuning the polarization of the incident laser field from linear to circular, second-harmonic measurements in TIs enable us to extract these explicit contributions from the band bending (Edc) and metallic surface states (�(2)), respectively. In this work, we report the relaxation dynamics of the differential change in SHG intensity (�I(�pp) = Ishgpump on(�pp) - Ishgpump off) with respect to the pump-probe delay time (�pp) in Bi2Te3 crystal, mainly emphasizing on different pump-probe polarization configurations to provide an understanding of the temporal evolution of �Edc(�pp) and ��(2)(�pp). Upon photoexcitation, �I(�pp) with linearly polarized pump-probe configuration, we observe two opposing contributions to �Edc, namely, the depletion electric field (DEF) and surface photovoltage (SPV) that effectively determine the spatial distribution of the bulk and surface carrier densities. However, on switching the probe polarization from linear to circular, we show that the SHG response has a predominant contribution from �(2), thereby extracting the time evolution of ��(2) arising from the TSS after photoexcitation, observed as an additional positive enhancement of �I(�pp). This is analytically understood by opening a band gap of �48 meV at the Dirac point due to the breaking of time reversal symmetry using circularly polarized light. © 2023 American Chemical Society.

Item Type:	Journal Article
Publication:	ACS Photonics
Publisher:	American Chemical Society
Additional Information:	The copyright for this article belongs to American Chemical Society
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	04 Mar 2024 09:14
Last Modified:	04 Mar 2024 09:14
URI:	https://eprints.iisc.ac.in/id/eprint/84303

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