We consider a quasi-two-dimensional gas of electrons in a typical Si-MOSFET, assuming repulsive contact interaction between electrons. Magnetisation and susceptibility are evaluated within the mean-field approach. Finite thickness of the inversion layer results in an interaction-induced electron wave function change, not found in both purely two-dimensional and three-dimensional (bulk) cases. Taking this self-consistent change into account leads to an increased susceptibility and ultimately to a ferromagnetic transition deep in the high-density metallic regime. We further find that in the paramagnetic state, magnetisation increases sublinearly with increasing in-plane magnetic field. In the opposite limit of low carrier densities, the effects of long-range interaction become important and can be included phenomenologically via bandwidth renormalisation. Our treatment then suggests that with decreasing density, the metal–insulator transition is preceded by a ferromagnetic instability. Results are discussed in the context of the available experimental data, and arguments for the validity of our mean-field scheme are presented.
Bibliographical noteFunding Information:
The author takes pleasure in thanking R. Berkovits, P. Coleman, B. D. Laikhtman, S. V. Kravchenko, I. Shlimak, L. D. Shvartsman, and R. Valenti for enlightening discussions. Discussions with the late K. A. Kikoin are gratefully acknowledged. This work was supported by the Israeli Absorption Ministry.
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- Magnetic properties