CT-X: An efficient continuous-time quantum Monte Carlo impurity solver in the Kondo regime

In the present paper, we present an efficient continuous-time quantum Monte Carlo impurity solver termed CT-X with high acceptance rate at low temperature for multi-orbital quantum impurity models with general interaction. In this hybridization expansion impurity solver, the imaginary time evolution operator for the high energy multiplets, which decays very rapidly with the imaginary time, is approximated by a probability normalized δ-function. As the result, the virtual charge fluctuations of fⁿ→f^n±1 are well included on the same footing without applying Schrieffer–Wolff transformation (SWT) explicitly. CT-X is proven to be equivalent to SWT on the leading order of W/U, where W is half the conduction band width and U is the local interaction strength. As benchmarks, our algorithm perfectly reproduces the results for both Coqblin–Schriffeer model and Kondo lattice model obtained by CT-J method developed by Otsuki et al. Furthermore, it allows capturing low energy physics of heavy-fermion materials directly without fitting the exchange coupling J in the Kondo model. Finally, we reformulate the dynamical mean-field theory loops using only the quasi-particle part of the f-electron Green's function measured in CT-X. Our benchmark calculations on CeIrIn5 at low temperature demonstrate a very reasonable low-energy f-electron density of states, which is in good agreement with the recent ARPES experiment.