Intrinsic gap of the T = 1 bilayer exciton condensate

P. GIUDICI; N. KUMADA; K. MURAKI

Kobe

Conferencia; Electronic Properties of Two-Dimensional Systems (EP2DS-18); 2009

Bilayer electron systems at total filling factor νT = 1 presents a new class of purely many-body quantum Hall (QH) state that emerges in the limit of strong interlayerinteractions, distinguished by possessing spontaneous interlayer phase coherence and a gap that opens at the Fermi level. Upon increasing the effective interlayer distance d/ℓB, the system undergoes a phase transition to a compressible state, characterized by the individual layer filling ν = 1/2. Recently, we have shown that, in the standard experimental conditions, the compressible state is only partially spin polarized, so that the position of the phase boundary strongly depends on the Zeeman energy. This suggests that the behavior of the νT = 1 QH state in the vicinity of the phase transition reported thus far may not represent the intrinsic property of the system. Here we report on the investigation of the quasiparticleenergy gap through activation measurements in a tilted magnetic field. The sample consists of a double quantum well with an interlayer distance d = 28 nm and negligible interlayer tunneling. When the Zeeman energy is increased by tilting the sample, we observe thatthe gap first increases with tilt reflecting the shift of the phase boundary and then saturates at large tilt. As a consequence, when the gap is plotted as a function of d/ℓB, all data in this saturation region, align on a single curve representing the intrinsic behavior of the gap,solely governed by d/ℓB. Furthermore, a simple mean-field model based on exciton formation provides, without adjustable parameters, an excellent description ofthe measured gap.