Beats of Quantum Oscillations of the Resistance in Two-Subband Electron Systems in Tilted Magnetic Fields

Electron transport in single GaAs quantum wells of widths from 22 to 46 nm with two populated quantum-confinement subbands E^S and E^AS is investigated at a temperature of T = 4.2 K in tilted magnetic fields B < 2 T. The angle α between the applied magnetic field and the normal to the plane of the structure under study is varied from 0° to 90°. In a perpendicular magnetic field (α = 0), magnetointersubband oscillations with a period determined by the relation Δ_SAS = E^AS - E^S = jħω_c, where ω_c is the cyclotron frequency and j is a positive integer, are observed in all investigated quantum wells. In tilted fields, the peaks of magnetointersubband oscillations are shifted toward higher fields B cos α. This shift is explained by an increase in the energy splitting Δ_SAS with increasing component B sin α. In 46- and 36-nm-wide quantum wells, beats of magnetointersubband oscillations are observed at angles α > 72° and α > 85°, respectively. The origin of this unexpected behavior of magnetointersubband oscillations in tilted magnetic fields is discussed.