Magneto-Inter-Subband Oscillations in GaAs quantum wells with three populated subbands placed in tilted magnetic fields.

The effect of tilted magnetic fields on magnetotransport is studied in GaAs quantum wells with three populated subbands. In perpendicular fields magneto-intersubband oscillations (MISO) are observed. These oscillations obey the relation $\Delta _{\mathbf{ij}} \quad =$\textbf{(E}$_{\mathbf{i}}$\textbf{-E}$_{\mathbf{j}}$\textbf{)}$=$\textbf{\textit{k}}\textbf{ž}$\omega _{\mathbf{c}}$, where \textbf{E}$_{\mathbf{i\, }}_{\, }$is the energy of the bottom of $i$-th subband and \textbf{\textit{k}} is an integer. MISO are periodic in the inverse magnetic field and show three frequencies \textbf{f}$_{\mathbf{ij\, }}$\textbf{\textasciitilde }$\Delta _{\mathbf{ij}}$\textbf{.} \quad Due to \textbf{E}$_{\mathbf{1,2}}$\textbf{\textless \textless E}$_{\mathbf{3}}$ two MISO oscillate at high frequencies (HF) demonstrating a beat pattern with the beat frequency \textbf{f}$_{\mathbf{b}} \quad =$\textbf{(f}$_{\mathbf{13}}$\textbf{-f}$_{\mathbf{23}}$\textbf{)/2\textasciitilde }$\Delta_{\mathbf{12}}$. With increasing tilt angle at small magnetic fields, \textbf{ž}$\omega_{\mathbf{c}}$\textbf{\textless }$\Delta _{\mathbf{12\, ,\, }}$the periodicity of HF-MISO changes indicating a change in the subband gap $\Delta_{\mathbf{12}}$\textbf{.} The dependence of $\Delta_{\mathbf{12\, }}$on the parallel magnetic field is found to be in a good agreement with existing theory. At larger parallel magnetic fields and \textbf{ž}$\omega_{\mathbf{c}}$\textbf{ \textgreater }$\Delta_{\mathbf{12\, ,\, }}$the high frequency beating disappears leaving only HF-MISO with single frequency \textbf{f}$=$\textbf{(f}$_{\mathbf{13}} \quad +$\textbf{f}$_{\mathbf{23}}$\textbf{)/2}.\textbf{ }It indicates a magnetic breakdown between the lower two subbands. Investigations of the 2D electron system in the regime of the magnetic breakdown are presented.