Dresden 2020 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 59: THz and MIR physics in semiconductors

HL 59.6: Talk

Thursday, March 19, 2020, 11:15–11:30, POT 151

Symmetry breaking and circular photogalvanic effect in epitaxial Cd_xHg_1−xTe films — Stefan Hubmann¹, Grigory Budkin², •Maximilian Otteneder¹, Dmitro But³, Daniel Sacré¹, Ivan Yahniuk³, Kilian Diendorfer¹, Vasily Bel’kov², Dmitry Kozlov⁴, Nikolay Mikhailov⁴, Sergey Dvoretsky⁴, Vasily Varavin⁴, Vladimir Remesnik⁴, Sergey Tarasenko², Wojciech Knap³, and Sergey Ganichev¹ — ¹Terahertz Center, University of Regensburg, Regensburg, Germany — ²Ioffe Institute, St. Petersburg, Russia — ³International Research Centre CENTERA, Institute of High Pressure Physics, Warsaw, Poland — ⁴Rzhanov Institute of Semiconductor Physics, Novosibirsk, Russia

We report on the observation of symmetry breaking and the circular photogalvanic effect (CPGE) in Cd_xHg_1−xTe alloys. We demonstrate that irradiation of bulk epitaxial films with circularly polarized terahertz radiation leads to the CPGE yielding a photocurrent whose direction reverses upon switching the photon helicity. This effect is forbidden in bulk zinc-blende crystals by symmetry arguments and, therefore, its observation indicates either symmetry reduction of the bulk material or that photocurrents are excited in topological surface states formed in alloys with low cadmium concentration. Bulk states play a crucial role since the CPGE is also clearly detected in samples with non-inverted band structure and therefore we suggest that strain is a reason of the symmetry reduction. We develop a theory of the CPGE showing that it results from quantum interference of different pathways contributing to the free-carrier absorption of radiation.