Modulation of bilayer quantum Hall states by tilted-field-induced subband-Landau-level coupling

Abstract

We study effects of tilted magnetic fields on energy levels in a double-quantum-well (DQW) system, focusing on the coupling of subbands and Landau levels (LLs). The subband-LL coupling induces anticrossings between LLs directly manifested in the magnetoresistance. The anticrossing gap becomes larger than the spin splitting at the tilting angle $\ensuremath{\theta}\ensuremath{\sim}20\ifmmode^\circ\else\textdegree\fi{}$ and larger than the cyclotron energy at $\ensuremath{\theta}\ensuremath{\sim}50\ifmmode^\circ\else\textdegree\fi{}$, demonstrating that the subband-LL coupling exerts a strong influence on quantum Hall states even at a relatively small $\ensuremath{\theta}$ and plays a dominant role for larger $\ensuremath{\theta}$. We also find that when the DQW potential is asymmetric, LL coupling occurs even within a subband. Calculations including higher-order coupling reproduce the experimental results quantitatively well.