Tunneling gap collapse and upsilon=2 quantum Hall state in a bilayer electron system - art. no. 045318

摘要

We have investigated the evolution of quantum Hall states in a GaAs-AlxGa1-xAs bilayer electron system by low-temperature magnetoresistivity measurements as the system was driven from a balanced to an off-balanced configuration. At low magnetic fields, odd integer filling factor quantum Hall states were observed on balance owing to the symmetric-antisymmetric tunneling gap. However, at high magnetic fields, in the regime of tunneling gap collapse, we observed anomalous quantum Hall states at v=2 off balance and v=3 on balance. At v=2, an energy gap was present all the way from the balanced configuration to far off balance, when only one quantum well was occupied. This is attributed to a transition from a spin-polarized state on balance to a spin-singlet state off balance, either by an abrupt exchange-driven phase transition or a continuous phase transition via a series of interlayer phase coherent states. [References: 26]