Symmetry breaking and circular photogalvanic effect in epitaxial CdxHg1−xTe films

Abstract

We report on the observation of symmetry breaking and the circular photogalvanic effect in Cdx Hg1-x Te alloys. We demonstrate that irradiation of bulk epitaxial films with circularly polarized terahertz radiation leads to the circular photogalvanic effect (CPGE) yielding a photocurrent whose direction reverses upon switching the photon helicity. This effect is forbidden in bulk zinc-blende crystals by symmetry arguments, therefore, its observation indicates either the symmetry reduction of bulk material or that the photocurrent is excited in the topological surface states formed in a material with low Cadmium concentration. We show that the bulk states play a crucial role because the CPGE was also clearly detected in samples with non-inverted band structure. We suggest that strain is a reason of the symmetry reduction. We develop a theory of the CPGE showing that the photocurrent results from the quantum interference of different pathways contributing to the free-carrier absorption (Drude-like) of monochromatic radiation. arXiv:1911.01936v1 [cond-mat.mes-hall]

Strain-induced circular photogalvanic current in Dirac semimetal Cd3As2 films epitaxied on a GaAs(111)B substrate

“…Though the extracted amplitude of the CPGE current is much smaller than that of the LPGE in the epitaxial Cd 3 As 2 film, the CPGE current generation efficiency, obtained by normalizing the measured CPGE current with respect to the corresponding excitation power, is as large as 15 nA mW −1 in the Cd 3 As 2 film at an incidence angle of 30°. This is much larger than that observed in other materials such as a GaAs/AlGaAs two-dimensional electron gas at room temperature at an incident angle of 30°(about 0.01 nA mW −1 ), 60 AlGaN/GaN superlattices at room temperature at an incident angle of 60°(about 0.06 nA mW −1 ), 63 Cd x Hg 1−x Te films at 4.2 K with normal incidence (about 4.5 nA mW −1 ), 64 etc. We further examined the CPGE response as a function of the incident angle to explore its generation nature.…”

Incident Angle Dependence of the Waveform of the Polarization-Sensitive Photoresponse in CuSe/Se Thin Film

“…It is of interest to study the laws governing the PSPC in various media in terms of excitation of spin-polarized electrons [15,16], for the creation and development of optospintronic devices [17], laser polarization analyzers [18][19][20], photodiodes with high spatial resolution [21], as well as for photosensors intended for the direct recording of the polarization state of circularly polarized light [22][23][24][25]. The mechanisms of the PSPC generation include the photogalvanic effect (PGE) [26][27][28], the circular photogalvanic effect (CPGE) [11,[29][30][31][32][33][34], the photon drag effect (PDE) [5,10,[35][36][37][38], and the surface photogalvanic effect (SPGE) [5,39,40]. All of the aforementioned effects are nonlinear optical phenomena.…”

“…The temporal profiles of those pulses strongly depend on the polarization ellipse of the incident femtosecond laser beam. However, despite the large number of articles on the topic of PSPC generation in various film materials (see, for example, [33,38,[49][50][51][52]), studies of the influence of the incidence angle on the waveforms of photocurrent pulses arising due to the PDE and SPGE (and also CPGE) under pulsed laser pumping have not been carried out yet.…”

Photoelectromagnetic Effect Induced by Terahertz Laser Radiation in Topological Crystalline Insulators Pb1−xSnxTe

“…Another experimental approach is optoelectronic probing of topological electron states, which may be insensitive to the bulk conductivity. Examples of such phenomena include the photogalvanic effect [15][16][17][18], the photon-drag effect [19], and photoconductivity [20][21][22]. One more example of this kind is the photoelectromagnetic (PEM) effect.…”