Effective g factor of low-density two-dimensional holes in a Ge quantum well

We report the measurements of the effective g factor of low-density two-dimensional holes in a Ge quantum well. Using the temperature dependence of the Shubnikov-de Haas oscillations, we extract the effective g factor in a magnetic field perpendicular to the sample surface. Very large values of the effective g factor, ranging from ∼13 to ∼28, are observed in the density range of 1.4×1010 cm-2- 1.4×1011 cm-2. When the magnetic field is oriented parallel to the sample surface, the effective g factor is obtained from a protrusion in the magneto-resistance data that signify full spin polarization. In the latter orientation, a small effective g factor, ∼1.3-1.4, is measured in the density range of 1.5×1010 cm-2- 2×1010 cm-2. This very strong anisotropy is consistent with theoretical predictions and previous measurements in other 2D hole systems, such as InGaAs and GaSb.