Abstract-Edge photocurrent driven by terahertz electric field in bilayer graphene

S. Candussio, M. V. Durnev, S. A. Tarasenko, J. Yin, J. Keil, Y. Yang, S. -K. Son, A. Mishchenko, H. Plank, V. V. Bel’kov, S. Slizovskiy, V. Fal’ko, and S. D. Ganichev

https://journals.aps.org/prb/accepted/2a075O28F8a1563cb8704928a7c656be3f612e62c

We report on the observation of edge electric currents excited in bi-layer graphene by terahertz laser radiation. We show that the current generation belongs to the class of second order in electric field phenomena and is controlled by the orientation of the THz electric field polarization plane. Additionally, applying a small magnetic field normal to the graphene plane leads to a phase shift in the polarization dependence. With increasing the magnetic field strength, the current starts to exhibit $1/B$-magnetooscillations with a period consistent with that of the Shubnikov-de Haas effect and amplitude by an order of magnitude larger as compared to the current at zero magnetic field measured under the same conditions. The microscopic theory developed shows that the current is formed in the edges vicinity limited by the mean-free path of carriers and the screening length of the high-frequency electric field. The current originates from the alignment of the free carrier momenta and dynamic accumulation of charge at the edges, where the $P$-symmetry is naturally broken. The observed magnetooscillations of the photocurrent are attributed to the formation of Landau levels.

Abstract-Infrared/terahertz spectra of the photogalvanic effect in (Bi,Sb)Te based three-dimensional topological insulators

H. Plank, J. Pernul, S. Gebert, S. N. Danilov, J. König-Otto, S. Winnerl, M. Lanius, J. Kampmeier, G. Mussler, I. Aguilera, D. Grützmacher, and S. D. Ganichev

https://journals.aps.org/prmaterials/abstract/10.1103/PhysRevMaterials.2.024202

We report on the systematic study of infrared/terahertz spectra of photocurrents in (Bi,Sb)Te based three-dimensional topological insulators. We demonstrate that in a wide range of frequencies, ranging from fractions up to tens of terahertz, the photocurrent is caused by the linear photogalvanic effect (LPGE) excited in the surface states. The photocurrent spectra reveal that at low frequencies the LPGE emerges due to free carrier Drude-like absorption. The spectra allow us to determine the room temperature carrier mobilities in the surface states despite the presence of thermally activated residual impurities in the material bulk. In a number of samples we observed an enhancement of the linear photogalvanic effect at frequencies between 30 and 60 THz, which is attributed to the excitation of electrons from helical surface to bulk conduction band states. Under this condition and applying oblique incidence we also observed the circular photogalvanic effect driven by the radiation helicity.

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