Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 111: Correlated Electrons: Quantum Impurities, Kondo Physics

TT 111.5: Talk

Friday, March 20, 2015, 10:30–10:45, H 3005

One- and two-particle impurity Green's functions obtained using worm sampling — •Markus Wallerberger¹, Patrik Gunacker¹, Emanuel Gull², Giorgio Sangiovanni³, and Karsten Held¹ — ¹TU Wien, Austria — ²University of Michigan, Ann Arbor MI, USA — ³Universität Würzburg, Germany

The single impurity Anderson model (SIAM) is one of the fundamental models of electronic correlation and lies at the computational core of dynamical mean field theory and diagrammatic extensions thereof. A state-of-the-art method for solving the SIAM is the continuous-time quantum Monte Carlo method in its hybridisation expansion (CT-HYB), because it is free of systematic bias and thus numerically exact.

In CT-HYB, one expands the partition function in terms of the hybridisation with the bath and stochastically sums the resulting diagrammatic series. The many-body propagators are usually obtained as a ``by-product'' of partition function sampling, as this allows for an easy implementation. We however show that this method leads to severe ergodicity problems for strong insulators and fails to yield spin-flip and pair-hopping terms of the vertex in high-symmetry cases.

Worm sampling avoids above complications by directly sampling the many-body propagators. We show that its use in CT-HYB significantly improves the quality and statistical uncertainties of the propagators. We also demonstrate how by using worm sampling for the impurity vertex, one can calculate frequency boxes of arbitrary sizes.