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 $\theta \sim 20°$ and larger than the cyclotron energy at $\theta \sim 50°$, demonstrating that the subband-LL coupling exerts a strong influence on quantum Hall states even at a relatively small $\theta$ and plays a dominant role for larger $\theta$. 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.

• Received 26 September 2007

DOI:https://doi.org/10.1103/PhysRevB.77.155324