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Magneto-intersubband resistance oscillations in GaAs quantum wells placed in a tilted magnetic field

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 ($E_1\approx E_2<<E_3$). At zero in-plane magnetic fields magneto-intersubband oscillations (MISO) between the $i^{th}$ and $j^{th}$ subbands are observed and obey the relation $Δ_{ij}=E_j-E_i=k\cdot\hbarω_c$, where $ω_c$ 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. At $\hbarω_c \ll Δ_{12}$ the in-plane magnetic field increases considerably the gap $Δ_{12}$, which is consistent with the semi-classical regime of electron propagation. In contrast at strong magnetic fields $\hbarω_c \gg Δ_{12}$ relatively weak oscillating variations of the electron spectrum with the in-plane magnetic field are observed. At $\hbarω_c \approx Δ_{12}$ 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 to $\hbarω_c \gg Δ_{12}$