Thermoelectric transport through a quantum dot: Effects of asymmetry in Kondo channels

Abstract

We consider effects of magnetic field on the thermopower and thermoconductance of a single-electron transistor based on a quantum dot strongly coupled to one of the leads by a single-mode quantum point contact. We show appearance of two new energy scales: ${T}_{\text{min}}\ensuremath{\sim}{|r|}^{2}{E}_{C}{(B/{B}_{C})}^{2}$ depending on a ratio of magnetic field $B$ and the field ${B}_{C}$ corresponding to a full polarization of point contact and ${T}_{\text{max}}\ensuremath{\sim}{|r|}^{2}{E}_{C}$ depending on a reflection amplitude $r$ and charging energy ${E}_{C}$. We predict that the behavior of thermoelectric coefficients is consistent with the Fermi-liquid theory at temperatures $T⪡{T}_{\text{min}}$ while crossover from non-Fermi-liquid regime associated with a two-channel Kondo effect to Fermi-liquid single-channel Kondo behavior can be seen at ${T}_{\text{min}}<T<{T}_{\text{max}}$.