Effective g factor of 2D holes in strained Ge quantum wells

The effective g-factor of 2D holes in modulation doped \mbox{p-SiGe/Ge/SiGe} structures was studied. The AC conductivity of samples with hole densities from $3.9\times {10}^{11}$~to $6.2\times {10}^{11}{\text{cm}}^{-2}$ was measured in perpendicular magnetic fields up to $8\text{ T}$ using a contactless acoustic method. From the analysis of the temperature dependence of conductivity oscillations, the ${\mathrm{g}}_{\perp }$-factor of each sample was determined. The ${\mathrm{g}}_{\perp }$-factor was found to be decreasing approximately linearly with hole density. This effect is attributed to non-parabolicity of the valence band.