Large many-body enhanced gap near the ν = 1 Landau level crossing in a dilute GaAs 2D hole system

At Landau level (LL) filling factor ν = 1, the ground state of a low-disorder, 2D electron system (2DES) can be a quantum Hall ferromagnet (QHF), a fully-spin-polarized state with a large energy gap for charge excitations, even in the absence of single-particle Zeeman splitting. Many-body enhancement of the ν = 1 gap and signatures of Skyrmions have indeed been observed in GaAs 2DESs [1]. In GaAs 2D hole systems (2DHSs), there are LL crossings at finite magnetic fields due to the strong spin-orbit coupling, offering a viable platform to study QHF and Skyrmions at certain filling factors. Here we report a study of the ν = 1 quantum Hall state in a high-mobility, dilute 2DHS. We measure the ν = 1 energy gap near the crossing of the lowest two LLs through magneto-transport measurement. We observe large ν = 1 gaps, significantly enhanced over the values calculated in a single-particle picture over a wide range of density in the vicinity of the LL crossing. The gap remains large even at the LL crossing, indicating a QHF ground state, and scales as the square-root of magnetic field, further supporting its many-body origin. However, no signature of Skyrmions is observed.

[1] D. K. Maude et al., Phys. Rev. Lett. 77, 4604 (1996).