Title: Fate of the spin-\frac{1}{2} Kondo effect in the presence of temperature gradients,
Abstract: We consider a strongly interacting quantum dot connected to two leads held at
quite different temperatures. Our aim is to study the behavior of the Kondo
effect in the presence of large thermal biases. We use three different
approaches, namely, a perturbation formalism based on the Kondo Hamiltonian, a
slave-boson mean-field theory for the Anderson model at large charging energies
and a truncated equation-of-motion approach beyond the Hartree-Fock
approximation. The two former formalisms yield a suppression of the Kondo peak
for thermal gradients above the Kondo temperature, showing a remarkably good
agreement despite their different ranges of validity. The third technique
allows us to analyze the full density of states within a wide range of
energies. Additionally, we have investigated the quantum transport properties
(electric current and thermocurrent) beyond linear response. In the
voltage-driven case, we reproduce the split differential conductance due to the
presence of different electrochemical potentials. In the temperature-driven
case, we observe a strongly nonlinear thermocurrent as a function of the
applied thermal gradient. Depending on the parameters, we can find nontrivial
zeros in the electric current for finite values of the temperature bias.
Importantly, these thermocurrent zeros yield direct access to the system's
characteristic energy scales (Kondo temperature and charging energy).