Kondo Effect in Electron Tunneling through Quantum Dots - Study with Quantum Monte Carlo Method

Based on the Quantum Monte Carlo (QMC) technique, we developed a method to calculate the tunneling conductance of the quantum dot systems for which the Kondo effect becomes important. The method computes the conductance directly from the current correlation function, and is applicable to the cases in which the calculation is not reduced to the computation of single particle Green's function. We compare the calculated conductance with experiments, and found good qualitative agreement. The temperature in experiments seems to be not low enough compared with the Kondo temperature in the mid region of the two paired Coulomb oscillation peaks. We studied the Zeeman field effect, and showed that the conductance is strongly suppressed when it has been enhanced by the Kondo effect. The conductance of an Aharonov-Bhom circuit including dots was also studied.