Magnetoconductivity of the two-dimensional electron gas occupying two size-quantization subbands is studied theoretically. When the bottoms of subbands are separated by an integer number of Landau levels, the staircases of Landau levels in both subbands are completely aligned. For such values of magnetic field the intersubband scattering is enhanced. As it was pointed out by Polyanovsky, this results in additional Shubnikov-de Haas oscillations of conductivity with magnetic field, with period depending on subband separation, and amplitude depending weakly on temperature, provided that a large number of Landau levels in each subband are occupied. In the calculation of conductivity we make use of the self-consistent Born approximation generalized to the case of two subbands. An analytical theory for the case of strong disorder and numerical results for the case of weak disorder are presented.
