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

Abstract

Spin-split heavy-hole gases in strained germanium quantum wells were characterized by polarisationresolved terahertz time-domain spectroscopy. Effective masses, carrier densities, g-factors, transport lifetimes, mobilities and Rashba 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-hole mobilities were enhanced to over1.5 10 6 cm 2 V −1 s −1 at 3 K. This high mobility enabled the observation of the optical quantum Hall effect at terahertz frequencies for spin-split two-dimensional heavy-holes, evidenced as plateaux in the transverse magnetoconductivity at even and odd filling factors.

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

“…Both m * and g * derive from the bulk band structure and quantum confinement, with their values being heavily influenced by carrier interactions. For Ge 2D holes, most measurements yield m * ∼ 0.07 − 0.1 m 0 , where m 0 is the free electron mass [8,[10][11][12][13][14]. However, g * for Ge 2D holes has not been studied extensively.…”

Quantum plateaus in dynamical Hall conductivity

“…Therefore the filling of these states will not change the Hall conductivity and plateau-like behavior will be retained, see Fig.1. The plateau-like behaviour in the terahertz region observed in [8,9,10] can be understood from the above mentioned point of view. The ratio ∆ 2 /ω 2 in the above mentioned terahertz experiments ω ∼ ω c could be less than 10 −3 [9].…”

High-frequency breakdown of the integer quantum Hall effect in GaAs/AlGaAs heterojunctions

“…A linear high-frequency Hall response is far from being completely understood for systems with parabolic electron bands (AlGaAs, Si, Ge). Experimentally, the Hall effect in the THz range was observed in GaAs/AlGaAs heterojunctions 12,13 and in Ge quantum wells 14 . The high-frequency data in Refs.…”

“…In Refs. [12,14] the Hall conductivity was measured using time-domain spectroscopy (TDS). In principle, TDS allows the Hall conductivity to be obtained at fixed frequencies, but the authors present the data averaged over a wide spectral range.…”