Enhanced circular photogalvanic effect in HgTe quantum wells in the heavily inverted regime

Abstract

HgTe-based quantum wells (QWs) possess very strong spin-orbit interaction (SOI) and have become an ideal platform for the study of fundamental SOI-dependent phenomena and the topological insulator phase. Circular photogalvanic effect (CPGE) in HgTe QWs is of great interest because it provides an effective optical access to probe the spin-related information of HgTe systems. However, the complex band structure and large spin-splitting of HgTe QWs makes it inadequate to analyze the experimental results of CPGE in HgTe QWs [B. Wittmann et al., Semicond. Sci. Technol. 25, 095005 (2010)] with reduced band models. Here, based on the realistic eight-band k · p Hamiltonian and combined with the density-matrix formalism, we present a detailed theoretical investigation of CPGE in (001)-oriented Hg0.3Cd0.7Te/HgTe/Hg0.3Cd0.7Te QWs. We find the CPGE currents in HgTe QWs in the heavily inverted regime are significantly enhanced due to the strong distortion of band dispersion at a certain range of the energy spectrum. This enhancement effect could offer an experimental certificate that the HgTe QW is in the heavily inverted phase (usually accompanied with the emergence of two-dimensional topological edge states), and could also be utilized in engineering the high efficiency ellipticity detector of infrared and terahertz radiation [S. N. Danilov et al., J. Appl. Phys. 105, 013106 (2009)]. Additionally, within the same theoretical framework, we also investigate the interplay effect of structure inversion asymmetry and bulk inversion asymmetry and the pure spin currents driven by linearly polarized light in HgTe QWs.

Polarization Controlled Photocurrent in Perovskite CsGeX3 (X = Cl, Br, I)

“…To date, CsGeX 3 (X = I, Br, Cl) halides have been the subject of particular interest applied in optoelectronics, including solar cells and photodetectors. − It has been noticed that CsGeX 3 stands out as the unique compound with demonstrated ferroelectricity corresponding to the noncentrosymmetric crystal structure, which would give rise to the coupling of ferroelectric polarization and photocurrent. − However, the underlying mechanism of ferroelectric-optical coupling remains an open question for further investigation. It is well-known that the photogalvanic effect (PGE) occurs in materials without spatial inversion symmetry under the illumination of polarized light, − so the structures are such designed or a small bias across the devices is applied to induce asymmetry in the real space electronic structure. ,− In CsGeX 3 , Ge atoms deviate from the octahedral center due to the presence of Ge 2+ lone pair electrons, which leads to spatial inversion symmetry breaking. The photogenerated carriers are therefore unevenly distributed in the conduction band, which results in a continuous photocurrent without the need for an external bias or temperature gradient .…”

Terahertz wave emission from the trigonal layered PtBi2

“…Dirac and Weyl semimetals), which have common features characterized by some band(s) with linear dispersion in k-space near the Fermi level (Weng et al, 2016;Armitage et al, 2018). Owing to the exotic electronic structures in TMs, giant nonlinear responses can be usually expected, such as second harmonic generation (Wu et al, 2017;Patankar et al, 2018;Hamh et al, 2016), nonlinear Hall effect (Ma et al, 2019), and photogalvanic effect (PGE) (Guan et al, 2017;Li et al, 2017). Particularly, on the excitation of the femtosecond (fs) laser pulses, the ultrafast photocurrents and the associated electromagnetic wave emission in the terahertz (THz) regime have attracted enormous attention recently in TMs (Sirica et al, 2019;Gao et al, 2020;Rees et al, 2020;Ni et al, 2021;Braun et al, 2016).…”

“…Particularly, on the excitation of the femtosecond (fs) laser pulses, the ultrafast photocurrents and the associated electromagnetic wave emission in the terahertz (THz) regime have attracted enormous attention recently in TMs (Sirica et al, 2019;Gao et al, 2020;Rees et al, 2020;Ni et al, 2021;Braun et al, 2016). Among the variety of origins triggering the ultrafast currents, those mechanisms associated with the crystal symmetry and topology of TMs have recently attracted intense attention (Sirica et al, 2019;Gao et al, 2020;Rees et al, 2020;Ni et al, 2021;Braun et al, 2016;Luo et al, 2021;Ma et al, 2021), such as PGE (Guan et al, 2017;Li et al, 2017) and photon drag effect (Shi et al, 2021;Karch et al, 2010). In addition, owing to the spin-momentum locking property emerging in TMs (Qi and Zhang, 2011;Hasan and Kane, 2010;Weng et al, 2016;Armitage et al, 2018), the charge current involving the bands with spin-nondegeneracy can be naturally spin-polarized and hence enables TMs to be a potential candidate in the spintronic applications.…”

High‐Frequency Nonlinear Transport and Photogalvanic Effects in 2D Topological Insulators

“…At higher frequencies, when mechanisms of the dc current formation originate from the asymmetry of optical transitions in the space, these effects are commonly named photogalvanic effects . The photogalvanic effects, discovered in 1970s in bulk pyroelectric and gyrotropic crystals, are extensively studied now in low‐dimensional semiconductor structures providing an access to symmetry of the structures, optical selection rules, energy spectrum, energy, momentum, and spin relaxation times of carriers, etc . They are also used to optically inject spin and valley currents controlled by light polarization.…”

“…The photogalvanic effects, discovered in 70s in bulk pyroelectric and gyrotropic crystals 47,48 , are extensively studied now in low-dimensional semiconductor structures providing an access to symmetry of the structures, optical selection rules, energy spectrum, energy, momentum, and spin relaxation times of carriers, etc. [49][50][51][52][53][54][55][56][57] . They are also used to optically inject spin [58][59][60][61][62] and valley 59,[63][64][65][66][67][68] currents controlled by light polarization.…”