Spin-splitting surface states of strained GaAs(001) and spontaneous spin current from breaking of twofold symmetry

We theoretically study the electronic structure and spin splitting of a strained GaAs(001) surface with broken twofold symmetry. We introduce a surface electron Hamiltonian of our model. By k·p theory, we qualitatively evaluate the electronic structure of GaAs(001) surface, demonstrating that the spin degeneracy of the bottom of the surface-state conduction bands is split. Additionally, by the spin current operator, we evaluate the spin current of electrons in the bottom of the surface-state conduction bands, demonstrating that for n-type GaAs the spin current flows in the parallel direction to a mirror plane spontaneously. This is a new mechanism to generate the spin current