Photogalvanic current in a double quantum well

We study the in-plane stationary current caused by phototransitions between the states of a double quantum well. The electric polarization of light has both vertical and in-plane components. The stationary current originates from the periodic vibration of electrons between two non-equivalent quantum wells caused by the normal component of the alternating electric field with simultaneous in-plane acceleration/deceleration by the in-plane component of electric field. The quantum mechanism of the stationary current is conditioned by in-plane transition asymmetry which appears due to the indirect phototransitions with the participation of impurity scattering. The photocurrent has a resonant character corresponding to the equality of the photon energy to the distance between subbands. It is found that the current appears as a response to the linear-polarized light.Comment: 6 pages, 2 figure

Linearity of the edge states energy spectrum in the 2D topological insulator

Linearity of the topological insulator edge state spectrum plays the crucial role for various transport phenomena. The previous studies found that this linearity exists near the spectrum crossing point, but did not determine how perfect the linearity is. The purpose of the present study is to answer this question in various edge states models. We examine Volkov and Pankratov (VP) model [1] for the Dirac Hamiltonian and the model of [2,3] (BHZ1) for the Bernevig, Hughes and Zhang (BHZ) Hamiltonian [4] with zero boundary conditions. It is found that both models yield ideally linear edge states. In the BHZ1 model the linearity is conserved up to the spectrum ending points corresponding to the tangency of the edge spectrum with the boundary of 2D states. In contrast, the model of[5] (BHZ2) with mixed boundary conditions for BHZ Hamiltonian and the 2D tight-binding (TB) model from [4] yield weak non-linearity.Comment: 5 pages, 4 figure

Friedel oscillations of the magnetic field penetration in systems with spatial quantization

The magnetic field, applied to a size-quantized system produces equilibrium persistent current non-uniformly distributed across the system. The distributions of dia- and paramagnetic currents and magnetic field in a quantum well is found. We discuss the possibility of observation of field distribution by means of NMR.Comment: 4 pages, 1 figure, uses nanosymp.sty. Accepted for 10th International Symposium "Nanostructures: Physics and Technology", St Petersburg, Russia, June 17-21(2002). The extended version, including the case of strip geometry submitted to "JETP Letters

Persistent and radiation-induced currents in distorted quantum rings

Persistent and radiation-induced currents in distorted narrow quantum rings are theoretically investigated. We show that ring distorsions can be described using a geometrical potential term. We analyse the effect of this term on the current induced by a magnetic flux (persistent current) and by a polarized coherent electromagnetic field (radiation-induced current). The strongest effects in persistent currents are observed for distorted rings with a small number of electrons. The distortion smoothes the current oscillations as a function of the magnetic flux and changes the temperature dependence of the current amplitude. For radiation-induced currents, the distortion induces an ac component in the current and affects its dependence on the radiation frequency and intensity

Photovoltage in curved 1D systems

Curvature of quantum wire results in intrasubband absorption of IR radiation that induces stationary photovoltage in presence of circular polarization. This effect is studied in ballistic (collisionless) and kinetic regimes. The consideration is concentrated on quantum wires with curved central part. It is shown, that if mean free path is shorter than length of the curved part the photovoltage does not depend on the wire shape, but on the total angle of rotation of wire tangent. It is not the case when mean free path is finite or large. This situation was studied for three specific shapes of wires: "hard angle", "open book" and "$\Omega$-like".Comment: 12 pages, 1 figur