Regensburg 2022 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 40: THz and MIR Physics in Semiconductors
HL 40.7: Talk
Friday, September 9, 2022, 11:30–11:45, H33
Nonlinear photocurrents induced by terahertz radiation in twisted bilayer graphene — •Stefan Hubmann1, Philipp Soul1, Giorgio di Battista2, Marcel Hild1, Kenji Watanabe3, Takashi Taniguchi3, Dmitri Efetov2, and Sergey Ganichev1 — 1Terahertz Center, University of Regensburg, 93040 Regensburg, Germany — 2ICFO, Castelldefels, Barcelona 08860, Spain — 3National Institute for Materials Science, 1-1 Namiki, Tsukuba 305-0044, Japan
We report on the observation of nonlinear photocurrent and photoconductivity in twisted bilayer graphene (tBLG) with twist angles below 1∘. We show that excitation of the tBLG bulk causes a photocurrent, whose sign and magnitude are controlled by the orientation of the radiation electric field and the photon helicity. The developed theory shows that the current is formed by asymmetric scattering in gyrotropic tBLG. For the observed photocurrents, we demonstrate the emergence of pronounced oscillations upon variation of the gate voltage, which correlate with the oscillations of the sample resistance. These photocurrent oscillations originate in interband transitions between a multitude of subbands in tBLG. Furthermore, at higher radiation intensities, we detected a nonlinear intensity dependence of bulk photogalvanic current and photoconductivity. These nonlinear photoresponses are caused by the interplay between interband, intersubband, and intraband transition. This interplay is controlled by the Fermi level position with respect to the Moiré subbands. We show that the photosignals saturate with rising intensity, while contributions from different transitions differ in their respective saturation behavior.