Spin thermopower in the overscreened Kondo model

Using the numerical renormalization group method, we study the spin thermopower in the two-channel spin-1/2 Kondo model. The non-Fermi liquid properties related to the overscreening of the impurity spin crucially affect the response of the system to the magnetic field and in consequence the spin-thermal transport. Although the magnetic field does not strongly polarize the impurity spin, we show that it nevertheless strongly affects the low-energy part of the spectral function. In turn, this leads to characteristic saturation of the spin Seebeck coefficient at the value of 0.388k(B)/vertical bar e vertical bar at T similar to T*, where T* proportional to B-2/T-K is the scale of the crossover between the intermediate-temperature non-Fermi-liquid regime and the low-temperature Fermi-liquid regime. We show that measuring the spin thermopower at low magnetic fields would provide a sensitive test for distinguishing regular Fermi liquid, singular Fermi liquid and non-Fermi liquid behaviour in nanodevices.