Interlayer Coherence in Bilayer Quantum Hall States

通过改变两个量子阱中的总电子密度和密度比，测量了填充因子ν=2和1的双层量子霍尔态的激活能。ν=1态在密度差的所有测量范围内都是稳定的。另一方面，随着电子密度的变化，ν=2态显示了这两种态之间的相变。ν=1态是被强层间库仑相互作用稳定的“相干”态。当层间库仑相互作用占主导地位时，ν=2态显示出从复合态到“相干”态的相变。这种ν=2“相干”态的出现是双层QH态自旋自由度的结果。我们通过倾斜样品测量了平衡点(n_f=n_b)的ν=2 QH态和单层点(n_fν=0，n_b=0)的≠=1 QH态的激活能。测量并比较了朗道能级填充因子ν=2时QH态和ν=1时单层QH态的第一次Skyrmion激发。在具有大隧道带隙的双层样品中，观察到的翻转自旋数为14个，在具有小隧道带隙的双层样品中为N_&lt；Spin&gt；=7，而在单层样品中为N_&lt；Spin&gt；=7。这种差异被解释为层间交换相互作用的结果。

The activation energy was measured in the bilayer quantum Hall (QH) state at filling factor ν = 2 and 1, by changing the total electron density and the density ratio in the two quantutn wells. The ν = 1 state is found stable over all measured range of the density difference. The ν = 2 state, on the other hand, shows a phase transition between these two types of the states as the electron density is changed. The ν = 1 state is a "coherent" state stabilarized by the strong interlayer Coulomb interaction. The ν = 2 state shows a phase transition from the compound state to the "coherent" state as the interlayer Coulomb interaction becomes dominant. The appearance of such ν = 2 "coherent" state is a consequence of the spin degree of freedom in the bilayer QH state.We have measured the activation energy of the ν = 2 QH state at the balanced point (n_f = n_b) and the ν = 1 QH state at the monolayer point (n_f ≠ 0, n_b = 0) by tilting the samples. Skyrmion excitations were measured and compared for the flrst time in the QH state at the Landau-level filling factor ν = 2 and in the monolayer QH state at ν = 1. The observed number of flipped spins, N_<spin>, is 14 in the bilayer sample with a large tunnelling gap, and N_<spin> = 7 in the bilayer sample with a small tunnelling gap, while it is N_<spin> = 7 in the monolayer sample. The difference is interpreted to be due to the interlayer exchange interaction.