Spontaneous spin polarization in quantum wires

Abstract

We have implemented self-consistent calculations of the electronic structure of quantum wires with an in-plane magnetic field parallel to the wire. Spin-density-functional theory of Kohn and Sham is applied. The self-consistent results show that full spontaneous spin polarization takes place in the low electron density regime, even at an arbitrary small magnetic field which demonstrates that the polarization is caused by exchange interactions. The results are consistent with recent measurements of a conductance anomaly in a quantum point contact. Moreover, it is remarkable that a large splitting of spin-related subbands occurs repeatedly whenever the Fermi energy passes the subband threshold energies, although the amplitude of the splitting becomes weaker as more subbands are occupied due to the screen effect. Self-consistent results indicate that a moderate magnetic field tends to suppress the spin polarization caused by the exchange interaction. The diamagnetic shift of the subbands is determined only for those which are close to the Fermi energy.