Spin properties of a two dimensional electron system: valley degeneracy and finite thickness effects

TL;DR

This paper calculates the spin susceptibility of two-dimensional electron systems considering valley degeneracy and finite thickness, comparing theoretical predictions with experiments across different device types.

Contribution

It applies the self-consistent mean-field STLS theory to analyze spin properties, highlighting the importance of device-specific parameters and identifying limitations in correlation treatment.

Findings

Good agreement with experiments for Si (100) systems

Predicts an abrupt spin-polarization transition at low densities

STLS theory's inaccuracies increase with more electron components

Abstract

The spin susceptibility of a two-dimensional electron system is calculated by determining the spin-polarization dependence of the ground-state energy within the self-consistent mean-field theory of Singwi et al. (STLS). Results are presented for three different devices, viz. the Si (100) inversion layer, the AlAs quantum well, and the GaAs heterojunction-insulated gate field-effect transistor. We find a fairly good agreement with experiments for the Si (100) system, on most of the experimental density range, whereas the agreement for the AlAs and GaAs systems is less satisfactory; in all cases, however, it is vital to include the characteristic device parameters like the valley degeneracy, the finite transverse thickness, etc. Further, the STLS theory predicts an abrupt spin-polarization transition at a sufficiently low electron density irrespective of the valley degeneracy and/or the finite thickness, with the partially spin-polarized states remaining unstable. Moreover, in the Si (100) inversion layer, the spin-polarization transition is preceded by the simultaneous valley- and spin- polarization; for its zero thickness model, these transitions however grossly disagree with the recent quantum Monte Carlo simulations. This drawback of the STLS theory is traced to its inaccuracy in treating electron correlations, which in turn become more and more important as the number of independent components (spin and valley) increases.