Quantum Transport Theory of Strongly Correlated Matter

TL;DR

This paper reviews advanced methods for calculating electric and thermal conductivities in strongly correlated materials, emphasizing approaches that handle complex interactions and scattering regimes beyond traditional approximations.

Contribution

It introduces novel formulas and computational techniques for magneto-conductivities that generalize Berry curvature and utilize thermodynamic averages, reducing computational complexity.

Findings

Validated methods on lattice electron and boson models.

Clarified the impact of strong interactions on transport near Mott insulators.

Demonstrated efficiency of Monte Carlo and variational techniques.

Abstract

This report reviews recent progress in computing Kubo formulas for general interacting Hamiltonians. The aim is to calculate electric and thermal magneto-conductivities in strong scattering regimes where Boltzmann equation and Hall conductivity proxies exceed their validity. Three primary approaches are explained. 1. Degeneracy-projected polarization formulas for Hall-type conductivities, which substantially reduce the number of calculated current matrix elements. These expressions generalize the Berry curvature integral formulas to imperfect lattices. 2. Continued fraction representation of dynamical longitudinal conductivities. The calculations produce a set of thermodynamic averages, which can be controllably extrapolated using their mathematical relations to low and high frequency conductivity asymptotics. 3. Hall-type coefficients summation formulas, which are constructed from thermodynamic averages. The thermodynamic formulas are derived in the operator Hilbert space formalism, which avoids the opacity and high computational cost of the Hamiltonian eigenspectrum. The coefficients can be obtained by well established imaginary-time Monte Carlo sampling, high temperature expansion, traces of operator products, and variational wavefunctions at low temperatures. We demonstrate the power of approaches 1--3 by their application to well known models of lattice electrons and bosons. The calculations clarify the far-reaching influence of strong local interactions on the metallic transport near Mott insulators. Future directions for these approaches are discussed.