L. E. Golub

Experimental Separation of Rashba and Dresselhaus Spin Splittings in Semiconductor Quantum Wells

The relative strengths of Rashba and Dresselhaus terms describing the spin-orbit coupling in semiconductor quantum well (QW) structures are extracted from photocurrent measurements on n-type InAs QWs containing a two-dimensional electron gas (2DEG). This novel technique makes use of the angular distribution of the spin-galvanic effect at certain directions of spin orientation in the plane of a QW. The ratio of the relevant Rashba and Dresselhaus coefficients can be deduced directly from experiment and does not relay on theoretically obtained quantities. Thus our experiments open a new way to determine the different contributions to spin-orbit coupling.

Giant spin relaxation anisotropy in zinc-blende heterostructures

Spin relaxation in-plane anisotropy is predicted for heterostructures based on zinc-blende semiconductors. It is shown that it manifests itself especially brightly if the two spin relaxation mechanisms (Dyakonov-Perel and Rashba) are comparable in efficiency. It is demonstrated that for the quantum well grown along the [001] direction, the main axes of spin relaxation rate tensor are [110] and

Rashba and Dresselhaus spin splittings in semiconductor quantum wells measured by spin photocurrents

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Demonstration of Rashba spin splitting in GaN-based heterostructures

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 -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.

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

Spin relaxation is investigated theoretically in two-dimensional systems. Various semiconductor structures of both n and p types are studied in detail. The most important spin relaxation mechanisms are considered. The spin relaxation times are calculated taking into account the contributions to the spin-orbit interaction due to the bulk inversion asymmetry and to the structure inversion asymmetry. It is shown that in-plane anisotropy of electron spin relaxation appears in III-V asymmetrical heterostructures. This anisotropy may be controlled by external parameters, and the spin relaxation times differ by several orders of magnitude.

Weak antilocalization in high-mobility two-dimensional systems

The circular photogalvanic effect, induced by infrared radiation, has been observed in (0001)-oriented n‐GaN low dimensional 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.

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

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.

Spin relaxation times of two-dimensional holes from spin sensitive bleaching of intersubband absorption

A 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. The obtained expressions are valid for both ballistic and diffusive regimes of weak localization. The 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.

Spin-splitting-induced photogalvanic effect in 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.