Spin thermopower in the overscreened Kondo model

R Žitko,T Rejec,A Ramšak,J Mravlje

doi:10.1088/1367-2630/15/10/105023

R Žitko, T Rejec + Show 2 more

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https://doi.org/10.1088/1367-2630/15/10/105023

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Abstract

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 0.388kB/|e| at T ∼ T*, where T*∝B2/TK 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.

Highlights

Using the numerical renormalization group method, we study the spin thermopower in the two-channel spin-1/2 Kondo model
We have analyzed the spin thermopower of the two-channel Kondo model, which is a paradigmatic case of an impurity model with non-Fermi-liquid properties at low-energy scales
We have shown that the crossover to the Fermi-liquid ground state generated by applied magnetic field B < TK leads to a pronounced peak in the spin Seebeck coefficient as a function of the temperature

Summary

Introduction

Using the numerical renormalization group method, we study the spin thermopower in the two-channel spin-1/2 Kondo model. We will show that the 2CK model exhibits very peculiar low-field behaviour of the spin thermopower, which has a maximum at the crossover scale T ∗ ∝ B2/TK with a height which saturates at small B (unlike in the fully screened and underscreened cases, where the height goes to zero). We plot the spin Seebeck coefficient of the 2CK model for a range of applied external magnetic fields B as a function of T .

Results

Conclusion