In-plane magnetic field effect on hole cyclotron mass and $g_z$ factor in high-mobility SiGe/Ge/SiGe structures

TL;DR

This study investigates how an in-plane magnetic field influences the hole cyclotron mass and $g_z$ factor in high-mobility Ge/SiGe quantum wells, revealing that the magnetic field increases the mass and decreases the $g_z$ factor, supported by a developed microscopic theory.

Contribution

The paper introduces a microscopic theory explaining the effects of in-plane magnetic fields on hole effective mass and $g_z$ factor in Ge/SiGe quantum wells, validated by experimental data.

Findings

In-plane magnetic field increases hole cyclotron mass.

In-plane magnetic field reduces the $g_z$ factor.

Experimental results align with the developed microscopic theory.

Abstract

The high-frequency (ac) conductivity of a high quality modulation doped GeSi/Ge/GeSi single quantum well structure with hole density $p$=6$\times$10$^{11}$cm$^{-2}$ was measured by the surface acoustic wave (SAW) technique at frequencies of 30 and 85~MHz and magnetic fields $B$ of up to 18 T in the temperature range of 0.3 -- 5.8 K. The acoustic effects were also measured as a function of the tilt angle of the magnetic field with respect to the normal of the two-dimensional channel at $T$=0.3 K. It is shown, that at the minima of the conductivity oscillations, holes are localized on the Fermi level, and that there is a temperature domain in which the high-frequency conductivity in the bulk of the quantum well is of the activation nature. The analysis of the temperature dependence of the conductivity at odd filling factors enables us to determine the effective $g_z$ factor. It is shown that the in-plane component of the magnetic field leads to an increase of the cyclotron mass and to a reduction of the $g_z$ factor. We developed a microscopic theory of these effects for the heavy-hole states of the complex valence band in quantum wells which describes well the experimental findings.