Magnetic field dependence of the thermopower of Kondo-correlated quantum dots

Abstract

Recent experiments have measured the signatures of the Kondo effect in the zero-field thermopower of strongly correlated quantum dots [Svilans {\em et al.,} Phys. Rev. Lett. {\bf 121}, 206801 (2018); Dutta {\em et al.,} Nano Lett. {\bf 19}, 506 (2019)]. They confirm the predicted Kondo-induced sign change in the thermopower, upon increasing the temperature through a gate-voltage dependent value $T_1\gtrsim T_{\mathrm{K}}$, where $T_{\mathrm{K}}$ is the Kondo temperature. Here, we use the numerical renormalization group (NRG) method to investigate the effect of a finite magnetic field $B$ on the thermopower of such quantum dots. We show that, for fields $B$ exceeding a gate-voltage dependent value $B_0$, an additional sign change takes place in the Kondo regime at a temperature $T_0(B\ge B_0)>0$ with $T_0<T_1$. The field $B_0$ is comparable to, but larger than, the field $B_c$ at which the zero-temperature spectral function splits in a magnetic field. The validity of the NRG results for $B_0$ are checked by comparison with asymptotically exact higher-order Fermi-liquid calculations [Oguri {\em et al.,} Phys. Rev. B {\bf 97}, 035435 (2018)]. Our calculations clarify the field-dependent signatures of the Kondo effect in the thermopower of Kondo-correlated quantum dots and explain the recently measured trends in the $B$-field dependence of the thermoelectric response of such systems [Svilans {\em et al.,} Phys. Rev. Lett. {\bf 121}, 206801 (2018)].

6 pages, 5 figures

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• Spin Seebeck effect of correlated magnetic molecules
• Charge and heat transport through quantum dots with local and correlated-hopping interactions
• Universality and thermoelectric transport properties of quantum dot systems
• Spin-orbit coupling effects over thermoelectric transport properties in quantum dots