Superlinear Photogalvanic Effects in (Bi0.3Sb0.7)2(Te

Abstract

We report on the observation of a complex nonlinear intensity dependence of the circular and linear photogalvanic currents induced by infrared radiation in compensated (Bi 0.3 Sb 0.7 ) 2 (Te 0.1 Se 0.9 ) 3 threedimensional topological insulators. The photocurrents are induced by direct optical transitions between topological surface and bulk states. We show that an increase in the radiation intensity results first in a highly superlinear rise in the amplitude of both types of photocurrents, whereas at higher intensities the photocurrent saturates. Our analysis of the observed nonlinearities shows that the superlinear behavior of the photocurrents is caused by heating of the electron gas, while the saturation is induced by slow relaxation of the photoexcited carriers, resulting in absorbance bleaching. The observed nonlinearities give access to the Fermi-level position with respect to the Dirac point and the energy relaxation times of Dirac fermions, providing an experimental room-temperature probe of topological surface states.

Terahertz spin ratchet effect in magnetic metamaterials

“…This is caused by the measurement setup where the j x and j y components are detected, i.e., the currents in the reflection plane (zx) and perpendicular to it. If, otherwise, the contacts are deposited along the pair of axes rotated by an angle Ψ to x, y then the additional phase 3Ψ appears in the expressions for the photocurrents which reflects the trigonal symmetry of the system [68,69].…”

“…(6) is the "trigonal" linear photogalvanic effect (LPGE) current j tr . It is present owing to asymmetrical scattering and has been studied in detail in intrinsically trigonal systems [68][69][70][71][72]. The system under study is extrinsically trigonal because of the presence of the artificially made macroscopic triangle antidots.…”

THz radiation induced circular Hall effect in graphene

“…For the terahertz radiation and in the used range of radiation intensities, the saturation of the photoconductivity response in gated samples is caused by the absorption bleaching [32,49,50]. The bleaching of the Drude-like radiation absorption in monolayer graphene has been recently studied by means of the nonlinear ultrafast [51] and photogalvanic [32] THz spectroscopy.…”

Epitaxial Growth of the BiySb2–yTe3–xSex 3D Topological Insulator: Physical Vapor Deposition and Molecular Beam Epitaxy

“…In the paper to reduce the mismatch between the film and the substrate, the 300 nm-thick BSTS films were grown by metalorganic vapor-phase epitaxy on sapphire through ZnTe buffer layers; however, they did not observe smooth surface relief. In spite of the fact that MBE allows one to vary the stoichiometry of compounds and precisely control layer thickness, the formation of BSTS films using MBE was also described only in several groups. , Expanding the number of compound components greatly complicates the growth procedure: it increases the degree of atomic disorder naturally occurring in these systems and reduces the number of suitable substrates since a large lattice constant mismatch stimulates the formation of crystal defects. The important processes responsible for a perfect BSTS film growth is, according to refs , passivation of dangling bonds on the substrate surface, a preliminary growth of the two-component buffer layer (Bi 2 Se 3 and Bi 2 Te 3 ), choosing the VI/V group partial pressure ratio θ and the growth rate ν.…”

“…In spite of the fact that MBE allows one to vary the stoichiometry of compounds and precisely control layer thickness, the formation of BSTS films using MBE was also described only in several groups. , Expanding the number of compound components greatly complicates the growth procedure: it increases the degree of atomic disorder naturally occurring in these systems and reduces the number of suitable substrates since a large lattice constant mismatch stimulates the formation of crystal defects. The important processes responsible for a perfect BSTS film growth is, according to refs , passivation of dangling bonds on the substrate surface, a preliminary growth of the two-component buffer layer (Bi 2 Se 3 and Bi 2 Te 3 ), choosing the VI/V group partial pressure ratio θ and the growth rate ν. To grow the Bi 2 Te 3 film with a desired composition from elemental sources, the coefficient θ usually varies in a wide range from 5 to 40. , In this case, the growth rate does not depend on tellurium but bismuth flux.…”