Kondo Effect in the Presence of Spin-Orbit Coupling

Recently, a series of noncentrosymmetric superconductors has been a subject of considerable interest since the discovery of superconductivity in CePt3Si. In noncentrosymmetric materials, the degeneracy of bands is lifted in the presence of spin-orbit coupling. This will bring about new effects in the Kondo effect since the band degeneracy plays an important role in the scattering of electrons by localized spins. We investigate the single-impurity Kondo problem in the presence of spin-orbit coupling. We examine the effect of spin-orbit coupling on the scattering of conduction electrons, by using the Green's function method, for the s-d Hamiltonian, with employing a decoupling procedure. As a result, we obtain a closed system of equations of Green's functions, from which we can calculate physical quantities. The Kondo temperature T-K is estimated from a singularity of Green's functions. We show that T-K is reduced as the spin-orbit coupling constant alpha is increased. When 2 alpha k(F) is comparable to or greater than k(B)T(K)(alpha = 0), T-K shows an abrupt decrease as a result of the band splitting. This suggests a Kondo collapse accompanied with a sharp decrease of T-K. The log T-dependence of the resistivity will be concealed by the spin-orbit interaction.