Spin degree of freedom in the bilayer nu=1 quantum Hall state

In a bilayer system at the total Landau level filling factor nu=1, when the interlayer correlation is strong, a many-body quantum Hall state supported by interlayer phase coherence occur. In this state, various interesting phenomena such as Josephson like interlayer tunneling and vanishing Hall resistance suggesting superfluidity have been observed. When the intralayer interactions dominate the interlayer ones, on the other hand, electrons in each layer configure monolayer nu=1/2 compressible state separately.
We investigate the phase transition between the QH and compound compressible states by nuclear spin relaxation measurements. We find that, as oppose to common assumption, electron spin degree of freedom is not frozen either in the QH or compressible states.
[Link]

>>back

Nuclear spin relaxation rate 1/T1 around bilayer nu=1 for several values of the magnetic field. When d/lB is small and the system is in the QH state, 1/T1 shows a minimum at nu=1. When d/lB is large and the system is in the compressible state, on the other hand, 1/T1 is maximum at nu=1. These results indicate that the electron spin state changes across the QH-compressible phase boundary.