An efficient continuous-time quantum Monte Carlo impurity solver in Kondo Regime

Changming Yue, Yilin Wang, Junya Otsuki +1 more

Emanuel Gull, Philipp Werner, Sebastian Fuchs +3 more

Junya Otsuki, Hiroaki Kusunose, Philipp Werner +1 more

An impurity solver based on a continuous-time quantum Monte Carlo method is developed for the Coqblin-Schrieffer model. The Monte Carlo simulation does not encounter a sign problem for antiferromagnetic interactions, and accurately reproduces the Kondo effect. Our algorithm can deal with an arbitrary number N of local degrees of freedom, becomes more efficient for larger values of N, and is hence suitable for models with orbital degeneracy. The dynamical susceptibility and the impurity t-matrix are derived with the aid of the Padé approximation for various values of N, and good agreement is found with other methods and available exact results. We point out that the Korringa-Shiba relation needs correction for a finite value of the exchange interaction.

Hartmut Hafermann, C. Jung, S. Brener +3 more

We present a very efficient solver for the general Anderson impurity problem. It is based on the perturbation around a solution obtained from exact diagonalization, using a small number of bath sites. We formulate a perturbation theory which is valid for both weak and strong coupling and interpolates between these limits. Good agreement with numerically exact quantum Monte Carlo results is found for a single bath site over a wide range of parameters. In particular, the Kondo resonance in the intermediate-coupling regime is well reproduced for a single bath site and the lowest-order correction. The method is particularly suited for low temperatures, alleviates analytical continuation of imaginary time data due to the absence of statistical noise and can be generalized to obtain dynamical quantities directly on the real axis.

Emanuel Gull, Philipp Werner, Olivier Parcollet +1 more

Hiroshi Shinaoka, Yusuke Nomura, Emanuel Gull