arXiv subjects

L. E. Golub

Publications and source records attributed to L. E. Golub.

At least 91 records · Page 5Linked to original sources

arXiv2009

Nonlinear magneto-gyrotropic photogalvanic effect

We report on the observation of nonlinear magneto-gyrotropic photogalvanic effect in HgTe/HgCdTe quantum wells. The interband absorption of mid-infrared radiation as well as the intrasubband absorption of terahertz radiation in the heterostructures is shown to cause a dc electric current in the presence of an in-plane magnetic field. A cubic in magnetic field component of the photocurrent is observed in quantum wells with the inverted band structure only. The experimental data are discussed in terms of both the phenomenological theory and microscopic models.

cond-mat.mes-hall↗

arXiv2009

Semiclassical theory of the photogalvanic effect in non-centrosymmetric systems

We develop a semiclassical theory of nonlinear transport and the photogalvanic effect in non-centrosymmetric media. We show that terms in semiclassical kinetic equations for electron motion which are associated with the Berry curvature and side jumps give rise to a dc current quadratic in the amplitude of the ac electric field. We demonstrate that the circular photogalvanic effect is governed by these terms in contrast to the linear photogalvanic effect and nonlinear I-V characteristics which are governed mainly by the skew scattering mechanism. In addition, the Berry curvature contribution to the magnetic-field induced photogalvanic effect is calculated.

cond-mat.mes-hall↗

arXiv2009

Tuning of structure inversion asymmetry by the $δ$-doping position in (001)-grown GaAs quantum wells

Structure and bulk inversion asymmetry in doped (001)-grown GaAs quantum wells is investigated by applying the magnetic field induced photogalvanic effect. We demonstrate that the structure inversion asymmetry (SIA) can be tailored by variation of the delta-doping layer position. Symmetrically-doped structures exhibit a substantial SIA due to impurity segregation during the growth process. Tuning the SIA by the delta-doping position we grow samples with almost equal degrees of structure and bulk inversion asymmetry.

cond-mat.mes-hall↗

arXiv2009

Spin-orbit interaction and weak localization in heterostructures

Theory of weak localization in two-dimensional high-mobility semiconductor systems is developed with allowance for the spin-orbit interaction. The obtained expressions for anomalous magnetoresistance are valid in the whole range of classically weak magnetic fields and for arbitrary strengths of bulk and structural inversion asymmetry contributions to the spin splitting. The theory serves for both diffusive and ballistic regimes of electron propagation taking into account coherent backscattering and nonbackscattering processes. The transition between weak localization and antilocalization regimes is analyzed. The manifestation of the mutual compensation of Rashba and Dresselhaus spin splittings in magnetoresistance is discussed. Perfect description of experimental data on anomalous magnetoresistance in high-mobility heterostructures is demonstrated. The in-plane magnetic field dependence of the conductivity caused by an interplay of the spin-orbit splittings and Zeeman effect is described theoretically.

cond-mat.mes-hall↗

arXiv2008

Fast detector of the ellipticity of infrared and terahertz radiation based on HgTe quantum well structures

We report a fast, room temperature detection scheme for the polarization ellipticity of laser radiation, with a bandwidth that stretches from the infrared to the terahertz range. The device consists of two elements, one in front of the other, that detect the polarization ellipticity and the azimuthal angle of the ellipse. The elements respectively utilise the circular photogalvanic effect in a narrow gap semiconductor and the linear photogalvanic effect in a bulk piezoelectric semiconductor. For the former we characterized both a HgTe quantum well and bulk Te, and for the latter, bulk GaAs. In contrast with optical methods our device is an easy to handle all-electric approach, which we demonstrated by applying a large number of different lasers from low power, continuous wave systems to high power, pulsed sources.

cond-mat.mes-hall↗

arXiv2008

Resonant circular photogalvanic effect in GaN/AlGaN heterojunctions

The resonant circular photogalvanic effect is observed in wurtzite (0001)-oriented GaN low-dimensional structures excited by infrared radiation. The current is induced by angular momentum transfer of photons to the photoexcited electrons at resonant inter-subband optical transitions in a GaN/AlGaN heterojunction. The signal reverses upon the reversal of the radiation helicity or, at fixed helicity, when the propagation direction of the photons is reversed. Making use of the tunability of the free-electron laser FELIX we demonstrate that the current direction changes by sweeping the photon energy through the intersubband resonance condition, in agreement with theoretical considerations.

cond-mat.mes-hall↗

arXiv2008

Quantum ratchet effects induced by terahertz radiation in GaN-based two-dimensional structures

Photogalvanic effects are observed and investigated in wurtzite (0001)-oriented GaN/AlGaN low-dimensional structures excited by terahertz radiation. The structures are shown to represent linear quantum ratchets. Experimental and theoretical analysis exhibits that the observed photocurrents are related to the lack of an inversion center in the GaN-based heterojunctions.

cond-mat.mes-hall↗

arXiv2008

Electric field control of spin-orbit splittings in GaAs/AlGaAs coupled quantum wells

Electron spin dynamics is investigated in n-i-n GaAs/AlGaAs coupled quantum wells. The electron spin dephasing time is measured as a function of an external electrical bias under resonant excitation of the 1sHH intrawell exciton using a time-resolved Kerr rotation technique. It is found a strong electron spin dephasing time anisotropy caused by an interference of the structure inversion asymmetry and the bulk inversion asymmetry. This anisotropy is shown to be controlled by an electrical bias. A theoretical analysis of electron spin dephasing time anisotropy is developed. The ratio of Rashba and Dresselhaus spin splittings is studied as a function of applied bias.

cond-mat.mes-hall↗

arXiv2007

Quantum and classical multiple scattering effects in spin dynamics of cavity polaritons

The transport properties of exciton-polaritons are studied with allowance for their polarization. Both classical multiple scattering effects and quantum effects such as weak localization are taken into account in the framework of a generalized kinetic equation. The longitudinal-transverse (TE-TM) splitting of polariton states which plays role analogous to the spin-orbit splitting in electron systems is taken into account. The developed formalism is applied to calculate the particle and spin diffusion coefficients of exciton-polaritons, spin relaxation rates and the polarization conversion efficiency under the conditions of the optical spin Hall effect. In contrast to the electron systems, strong spin splitting does not lead to the antilocalization behavior of the particle diffusion coefficient, while quantum corrections to spin diffusion and polarization conversion can be both negative and positive depending on the spin splitting value.

cond-mat.mes-hall↗

arXiv2007

Magneto-gyrotropic photogalvanic effects in GaN/AlGaN two-dimensional systems

The magneto-gyrotropic photogalvanic and spin-galvanic effects are observed in (0001)-oriented GaN/AlGaN heterojunctions excited by terahertz radiation. We show that free-carrier absorption of linearly or circularly polarized terahertz radiation in low-dimensional structures causes an electric photocurrent in the presence of an in-plane magnetic field. Microscopic mechanisms of these photocurrents based on spin-related phenomena are discussed. Properties of the magneto-gyrotropic and spin-galvanic effects specific for hexagonal heterostructures are analyzed.

cond-mat.mes-hall↗

arXiv2006

Rashba and Dresselhaus Spin-Splittings in Semiconductor Quantum Wells Measured by Spin Photocurrents

The spin-galvanic effect and the circular photogalvanic effect induced by terahertz radiation are applied to determine the relative strengths of Rashba and Dresselhaus band spin-splitting in (001)-grown GaAs and InAs based two dimensional electron systems. We observed that shifting the $δ$-doping plane from one side of the quantum well to the other results in a change of sign of the photocurrent caused by Rashba spin-splitting while the sign of the Dresselhaus term induced photocurrent remains. The measurements give the necessary feedback for technologists looking for structures with equal Rashba and Dresselhaus spin-splittings or perfectly symmetric structures with zero Rashba constant.

cond-mat.mes-hall↗

arXiv2006

Interplay of Rashba and Dresselhaus spin splittings in 2D weak localization

The effects of structural (Rashba) and bulk (Dresselhaus) spin-orbit interaction terms on the low-field magnetoresistance are investigated in high-quality two dimensional systems. The weak localization theory accounting for both of these terms valid in the whole range of magnetic fields is proposed. The suppresion of antilocalization correction as Rashba and Dresselhaus terms strengths approach each other is demonstrated. The effect of cubic in the wavevector spin-splitting term is analyzed.

cond-mat.mes-hall↗

arXiv2006

Spin and valley-orbit splittings in SiGe/Si heterostructures

Spin and valley-orbit splittings are calculated in SiGe/Si/SiGe quantum wells (QWs) by using the tight-binding approach. In accordance with the symmetry considerations an existence of spin splitting of electronic states in perfect QWs with an odd number of Si atomic planes is microscopically demonstrated. The spin splitting oscillates with QW width and these oscillations related to the inter-valley reflection of an electron wave from the interfaces. It is shown that the splittings under study can efficiently be described by an extended envelope-function approach taking into account the spin- and valley-dependent interface mixing. The obtained results provide a theoretical base to the experimentally observed electron spin relaxation times in SiGe/Si/SiGe QWs.

cond-mat.mes-hall↗

arXiv2006

Observation of Spin Relaxation Anisotropy in Semiconductor Quantum Wells

Spin relaxation of two-dimensional electrons in asymmetrical (001) AlGaAs quantum wells are measured by means of Hanle effect. Three different spin relaxation times for spins oriented along [110], [1-10] and [001] crystallographic directions are extracted demonstrating anisotropy of D'yakonov-Perel' spin relaxation mechanism. The relative strengths of Rashba and Dresselhaus terms describing the spin-orbit coupling in semiconductor quantum well structures. It is shown that the Rashba spin-orbit splitting is about four times stronger than the Dresselhaus splitting in the studied structure.

cond-mat.mes-hall↗

arXiv2005

Demonstration of Rashba spin splitting in GaN-based heterostructures

The circular photogalvanic effect (CPGE), induced by infrared radiation, has been observed in (0001)-oriented GaN quantum well (QW) structures. The photocurrent changes sign upon reversing the radiation helicity demonstrating the existence of spin-splitting of the conduction band in k-space in this type of materials. The observation suggests the presence of a sizeable Rashba type of spin-splitting, caused by the built-in asymmetry at the AlGaN/GaN interface.

cond-mat.other↗

arXiv2005

Weak antilocalization in high-mobility two-dimensional systems

Theory of weak antilocalization is developed for high-mobility two-dimensional systems. Spin-orbit interaction of Rashba and Dresselhaus types is taken into account. Anomalous magnetoresistance is calculated in the whole range of classically weak magnetic fields and for arbitrary strength of spin-orbit splitting. Obtained expressions are valid for both ballistic and diffusive regimes of weak localization. Proposed theory includes both backscattering and nonbackscattering contributions to the conductivity. It is shown that magnetic field dependence of conductivity in high-mobility structures is not described by earlier theories.

cond-mat.mes-hall↗

arXiv2004

Can an electric current orient spins in quantum wells?

A longstanding theoretical prediction is the orientation of spins by an electrical current flowing through low-dimensional carrier systems of sufficiently low crystallographic symmetry. Here we show by means of terahertz transmission experiments through two-dimensional hole systems a growing spin orientation with an increasing current at room temperature.

cond-mat.mes-hall↗

arXiv2004

Spin relaxation times of 2D holes from spin sensitive bleaching of inter-subband absorption

We present spin relaxation times of 2D holes obtained by means of spin sensitive bleaching of the absorption of infrared radiation in p-type GaAs/AlGaAs quantum wells (QWs). It is shown that the saturation of inter-subband absorption of circularly polarized radiation is mainly controlled by the spin relaxation time of the holes. The saturation behavior has been determined for different QW widths and in a wide temperature range with the result that the saturation intensity substantially decreases with narrowing of the QWs. Spin relaxation times are derived from the measured saturation intensities by making use of calculated (linear) absorption coefficients for direct inter-subband transitions. It is shown that spin relaxation is due to the D'yakonov-Perel' mechanism governed by hole-hole scattering. The problem of selection rules is addressed.

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