Quantum interferometry and spin-orbit effects in a heterostructure with a 2D hole gas in a Si0.2Ge0.8 quantum well

The magnetic-field dependence (up to 110 kOe) of the resistance of Si0.7Ge0.3/Si0.2Ge0.8/Si0.7Ge0.3 with a 2D hole gas in a Si0.2Ge0.8 quantum well is measured in the temperature range 0.335-10 K and in a range of variation of the currents from 100 nA to 50 muA. Shubnikov-de Haas oscillations are observed in the region of high magnetic fields, and in the low-field region Hless than or equal to1 kOe a positive magnetoresistance is observed which gives way to a negative magnetoresistance as the field is increased. This peculiarity is explained by effects of weak localization of the 2D charge carriers under conditions when the spin-orbit scattering time tau(so) is close to the inelastic scattering time tau(Phi), and it is evidence of a splitting of the spin states under the influence of a perturbing potential due to the formation of a two-dimensional potential well (the Rashba mechanism). Analysis of the weak localization effects gave the values of the characteristic relaxation times as tau(Phi)=7.2T(-1)x10(-12) s and tau(so)=1.36x10(-12) s. From these characteristics of the heterostructure studied, a value of Delta=2.97 meV was obtained for the spin splitting. (C) 2003 American Institute of Physics.