Effective Mass and Spin Susceptibility of Dilute Two-Dimensional Holes in GaAs

We report effective hole mass ($m^{*}$) measurements through analyzing the temperature dependence of Shubnikov-de Haas oscillations in dilute (density $p \sim 7 \times 10^{10}$ cm$^{-2}$, $r_{s} \sim 6$) two-dimensional (2D) hole systems confined to a 20 nm-wide, (311)A GaAs quantum well. The holes in this system occupy two nearly-degenerate spin subbands whose $m^{*}$ we measure to be $\sim $ 0.2 (in units of the free electron mass). Despite the relatively large $r_{s}$ in our 2D system, the measured $m^{*}$ is in good agreement with the results of our energy band calculations which do not take interactions into account. We hen apply a sufficiently strong parallel magnetic field to fully depopulate one of the spin subbands, and measure $m^{*}$ for the populated subband. We find that this latter $m^{*}$ is surprisingly close to the $m^{*}$ we measure in the absence of the parallel field. We also deduce the spin susceptibility of the 2D hole system from the depopulation field, and conclude that the susceptibility is enhanced by about 50% relative to the value expected from the band calculations.