Terahertz quantum Hall effect for spin-split heavy-hole gases in strained Ge quantum wells

Spin-split heavy-hole gases in strained germaniumquantumwells were characterized by polarisationresolved terahertz time-domain spectroscopy. Effectivemasses, carrier densities, g-factors, transport lifetimes,mobilities andRashba spin-splitting energies were evaluated, giving quantitative insights into the influence of strain. The Rashba coefficient was found to lower for samples with higher biaxial compressive strain, while heavy-holemobilities were enhanced to over ́ 1.5 106 cm V s at 3 K. This highmobility enabled the observation of the optical quantumHall effect at terahertz frequencies for spin-split two-dimensional heavy-holes, evidenced as plateaux in the transversemagnetoconductivity at even and oddfilling factors.