Third-order strong-coupling impurity solver for real-frequency DMFT: Accurate spectral functions for antiferromagnetic and photo-doped states

TL;DR

This paper introduces a third-order strong-coupling impurity solver using QTCI for accurate real-frequency spectral functions in DMFT, applicable to equilibrium and non-equilibrium states.

Contribution

The paper develops a novel third-order impurity solver employing QTCI, enabling precise real-frequency spectral calculations without analytical continuation.

Findings

Accurately captures spectral functions for antiferromagnetic states.

Effectively handles photo-doped states in Hubbard model.

Defines the interaction and temperature ranges for the method's validity.

Abstract

We present a real-frequency third-order strong-coupling impurity solver which employs quantics tensor cross interpolation (QTCI) for an efficient evaluation of the diagram weights. Applying the method to dynamical mean-field theory (DMFT) calculations of the single-band Hubbard model on the Bethe lattice, we clarify the interaction and temperature range in which the third-order approach yields accurate results. Since the calculations are implemented on the real-time/frequency axis, the detailed structure of spectral functions can be obtained without analytical continuation, as we demonstrate with examples for paramagnetic, antiferromagnetic and photo-doped states. Our work establishes a viable path toward high-order, real-frequency impurity solvers for both equilibrium and non-equilibrium DMFT studies.