Kondo Photo-Assisted Transport in Quantum Dots
The competition between electron-electron interaction and quantum mechanical hybridization between the delocalized electrons in a non-magnetic metal and the unpaired electrons of a magnetic impurity leads to the Kondo effect . It has been predicted , and recently observed experimentally ,  that the transport at low temperatures through a quantum dot (QD) coupled by tunneling barriers to two leads containing Fermi liquids is governed by a Kondo-like singularity existing in the quasiparticle density of states (DOS) at the Fermi level F of the leads. The physics behind such a behavior is well described by the low energy excitations of the Anderson Hamiltonian. When one electron at F, becomes scattered by the dot its wave function suffers a phase shift which is proportional to the exact QD displaced charge (DC). As a consequence of this Friedel-Langreth (FL) theorem  the conductance takes the value G = 2e 2/h sin 2(π〈δ(nσ)〉) where 〈δ(nσ)〉 is the DC , .
In this work we have generalized the Friedel-Langreth sum rule  to the case with AC potentials at finite temperature. We study the photoassisted transport through QD taking especial care in the fulfillment of this generalized rule. New features are found in the transport properties due to the AC potentials. We study the behaviour of the density of states in presence of AC potentials at temperature below and above of the Kondo temperature. The effect of the AC potential on both the quantum dot density of states and the linear conductance shows the importance of using a theory which describes intradot finite interaction and nonperturbative effects at finite temperature. In conclusion, our model considers, for the first time, finite U as well as charge conservation through the extension of the FL sum rule at finite temperature.
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