Magnetoresistance and spin polarization in the insulating regime of a Si two-dimensional electron system

TL;DR

This study investigates magnetoresistance and spin polarization in a high-mobility silicon 2D electron system at low electron densities, revealing persistent Landau level features and absence of ferromagnetic instability in the insulating regime.

Contribution

It provides new insights into the behavior of magnetoresistance and spin polarization in the insulating regime of silicon 2D electron systems, especially at very high resistivities.

Findings

Landau level features persist at high resistivity (~10^8 Ω).

No evidence of ferromagnetic instability in the insulating regime.

Magnetoresistance behavior indicates stable spin polarization without ferromagnetic transition.

Abstract

We have studied the magnetoresistance in a high-mobility Si inversion layer down to low electron concentrations at which the longitudinal resistivity $\rho_{xx}$ has an activated temperature dependence. The angle of the magnetic field was controlled so as to study the orbital effect proportional to the perpendicular component $B_\perp$ for various total strengths $B_{\rm tot}$. A dip in $\rho_{xx}$, which corresponds to the Landau level filling factor of $\nu=4$, survives even for high resistivity of $\rho_{xx} \sim 10^8 \Omega$ at $T= 150 {\rm mK}$. The linear $B_{\rm tot}$-dependence of the value of $B_\perp$ at the dip for low $B_{\rm tot}$ indicates that a ferromagnetic instability does not occur even in the far insulating regime.