Magnetointersubband resistance oscillations in GaAs quantum wells placed in a tilted magnetic field

The magnetotransport of highly mobile two-dimensional electrons in wide GaAs single quantum wells with three populated subbands placed in tilted 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 $({E}₁\ensuremath{\approx}{E}₂\ensuremath{\ll}{E}₃)$. At zero in-plane magnetic fields, magnetointersubband oscillations (MISO) between the $i\text{th}$ and $j\text{th}$ subbands are observed and obey the relation ${\mathrm{\ensuremath{\Delta}}}_ij={E}_j\ensuremath{-}{E}_i=k\ensuremath{\hbar}{\ensuremath{\omega}}_c$, where ${\ensuremath{\omega}}_c$ 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 $\ensuremath{\hbar}{\ensuremath{\omega}}_c\ensuremath{\ll}{\mathrm{\ensuremath{\Delta}}}₁₂$, the in-plane magnetic field increases considerably the gap ${\mathrm{\ensuremath{\Delta}}}₁₂$, which is consistent with the semiclassical regime of electron propagation. In contrast, at strong magnetic fields $\ensuremath{\hbar}{\ensuremath{\omega}}_c\ensuremath{\gg}{\mathrm{\ensuremath{\Delta}}}₁₂$ relatively weak oscillating variations of the electron spectrum with the in-plane magnetic field are observed. At $\ensuremath{\hbar}{\ensuremath{\omega}}_c\ensuremath{\approx}{\mathrm{\ensuremath{\Delta}}}₁₂$, 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 $\ensuremath{\hbar}{\ensuremath{\omega}}_c\ensuremath{\gg}{\mathrm{\ensuremath{\Delta}}}₁₂$.