Spin-independent effective mass in a valley-degenerate electron system

TL;DR

This paper demonstrates that in a valley-degenerate electron system, the effective mass remains spin-independent due to a collective plasmon mechanism, aligning with experimental observations in two-dimensional heterostructures.

Contribution

It introduces a model showing that in the large-N limit, the electron effective mass is independent of spin polarization, contrary to traditional expectations.

Findings

Mass enhancement via plasmon emission/absorption

Mass does not depend on polarization at leading order in 1/N

Small corrections for N=2, consistent with experiments

Abstract

In a generic spin-polarized Fermi liquid, the masses of spin-up and spin-down electrons are expected to be different and to depend on the degree of polarization. This expectation is not confirmed by the experiments on two-dimensional heterostructures. We consider a model of an $N$-fold degenerate electron gas. It is shown that in the large-N limit, the mass is enhanced via a polaronic mechanism of emission/absorption of virtual plasmons. As plasmons are classical collective excitations, the resulting mass does not depend on $N$, and thus on polarization, to the leading order in 1/N. We evaluate the 1/N corrections and show that they are small even for N=2.