Abstract
We demonstrate that a local moment can automatically form in the vicinity of the quantum point contact if we (1) include the spin-orbit interaction and (2) allow the electric field along the longitudinal direction to be both nonuniform and asymmetric. The former breaks the spin degeneracy by introducing an effective magnetic field while the latter ensures that the moment is formed near the point contact where the nonuniformity is the largest. The asymmetry induced by the source-drain bias leads to an imbalance of spin-up and spin-down electrons on different sides of the point contact, which introduces a spin polarization. The nonequilibrium Green's-function formalism is employed to study the transport properties and local spin density. The electron-electron interaction is found to enhance the magnitude of the localized moment, necessary for the Kondo-type scenario of the 0.7 anomaly. © 2010 The American Physical Society.