The magnetotransport of highly mobile 2D electrons in wide GaAs single quantum wells with three populated subbands placed in titled magnetic fields is studied. The bottoms of the lower two subbands have nearly the same energy while the bottom of the third subband has a much higher energy (E1 ≈ E2 << E3). At zero in-plane magnetic fields magneto-intersubband oscillations (MISO) between the i th and j th subbands are observed and obey the relation ∆ij = Ej −Ei = k·hωc, where ωc is the cyclotron frequency and k is an integer. An application of in-plane magnetic field produces dramatic changes in MISO and the corresponding electron spectrum. Three regimes are identified. Athωc ≪ ∆12 the in-plane magnetic field increases considerably the gap ∆12, which is consistent with the semi-classical regime of electron propagation. In contrast at strong magnetic fieldshωc ≫ ∆12 relatively weak oscillating variations of the electron spectrum with the in-plane magnetic field are observed. Athωc ≈ ∆12 the electron spectrum undergoes a transition between these two regimes through magnetic breakdown. In this transition regime MISO with odd quantum number k terminate, while MISO corresponding to even k evolve continuously into the high field regime corresponding tohωc ≫ ∆12.

The magnetotransport of highly mobile 2D electrons is studied in GaAs single quantum wells with three occupied subbands. The bottoms of the lower two subbands have nearly the same energy while the bottom of the third subband has a much higher energy (E1 ≈ E2 << E3). Magnetointersubband oscillations (MISO) between the i th and j th subbands are observed and obey the relation ∆ij = Ej − Ei = l •hωc, where ωc is the cyclotron frequency and l is an integer. The slight difference in the energies of the lower subbands produces noticeable interference effects in the magnetoresistance. In contrast to the case of two populated subbands, by analyzing the amplitude of each component of the MISOs separately, the quantum lifetime τ (i) q of electrons in i th subband is extracted. The studies show that τ (1) q ≈ τ (2) q = τ (1,2) q. The temperature variation of 1/τ (1,2) q is found to be proportional to T 2 indicating that the electron-electron interaction is the dominant source of the decrease of the electron lifetime at high temperatures. Different temperature dependence of the quantum scattering rate is found in the third subband, δ(1/τ (3) q) ∼ T , which is consistent with the theory of sparsely populated subbands.

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