Non-Fermi-liquid phases in the two-band Hubbard model: Finite-temperature exact diagonalization study of Hund's rule coupling

TL;DR

This study uses finite-temperature exact diagonalization within DMFT to explore non-Fermi-liquid phases in a two-band Hubbard model, revealing how Hund's coupling influences electronic behavior and phase transitions.

Contribution

It demonstrates the effectiveness of finite-temperature ED/DMFT in capturing Hund's exchange effects and finite-size impacts, providing insights beyond traditional QMC methods.

Findings

Identification of an intermediate mixed phase with distinct subband behaviors.

Finite lifetime at the Fermi level depends on Hund's coupling treatment.

Good agreement with NRG and previous QMC/DMFT results.

Abstract

The two-band Hubbard model involving subbands of different widths is investigated via finite-temperature exact diagonalization (ED) and dynamical mean field theory (DMFT). In contrast to the quantum Monte Carlo (QMC) method which at low temperatures includes only Ising-like exchange interactions to avoid sign problems, ED permits a treatment of Hund's exchange and other onsite Coulomb interactions on the same footing. The role of finite-size effects caused by the limited number of bath levels in this scheme is studied by analyzing the low-frequency behavior of the subband self-energies as a function of temperature, and by comparing with numerical renormalization group (NRG) results for an effective one-band model. For half-filled, non-hybridizing bands, the metallic and insulating phases are separated by an intermediate mixed phase with an insulating narrow and a bad-metallic wide subband. The wide band in this phase exhibits different degrees of non-Fermi-liquid behavior, depending on the treatment of exchange interactions. Whereas for complete Hund's coupling, infinite lifetime is found at the Fermi level, in the absence of spin-flip and pair-exchange, this lifetime becomes finite. Excellent agreement is obtained both with new NRG and previous QMC/DMFT calculations. These results suggest that-finite temperature ED/DMFT might be a useful scheme for realistic multi-band materials.