Evidence of breakdown of the spin symmetry in diluted 2D electron gases

Abstract

Direct evidence of spin polarisation in dilute two-dimensional electron gases formed in modulation-doped single quantum wells has been obtained from resonant inelastic light scattering. The abrupt enhancement of the exchange-correlation energy of collective intersubband spin and charge excitations observed at very low occupations of the second subband is the signature of the breakdown of the spin symmetry. Calculations of the elementary excitations within the time-dependent local spin-density approximation provide an explanation for the striking behaviour of the different terms of the Coulomb interaction and predict the existence of a ferromagnetic ground state in the very diluted regime.