Temperature-induced transport asymmetry around half-filling in high Landau levels*

We report a temperature dependence study of transport properties in an ultra-low disorder GaAs two-dimensional electron system around half-filling of the N = 2 Landau level. In this study, we performed measurements of both the zero-bias magnetoresistance R_xx and the differential resistance dV_xx/dI along the hard transport direction around filling factor ν = 9/2 at different temperatures. At high temperature, T = 100 mK, both R_xx and dV_xx/dI are symmetric around ν = 9/2. However, as temperature is decreased towards T = 10 mK both R_xx and dV_xx/dI become asymmetric: the R_xx peak shifts to lower magnetic field away from exact half-filling, and dV_xx/dI shows strong non-linearity on the high field side of the R_xx peak. Our data suggests that a temperature induced breakdown of particle-hole symmetry occurs at low temperatures. At high temperature T = 100 mK where the system behaves as a standard anisotropic nematic, particle-hole symmetry is restored.