Mott transitions in correlated electron systems with orbital degrees of freedom

TL;DR

This paper investigates Mott metal-insulator transitions in orbitally degenerate Hubbard models using a generalized dynamical mean-field theory, revealing how orbital degeneracy and Hund's coupling influence the critical interaction and transition nature.

Contribution

It introduces an efficient method to determine the critical interaction U_c for various fillings and degeneracies, highlighting the effects of Hund's rule exchange on transition behavior.

Findings

U_c scales linearly with orbital degeneracy M at half-filling.

Including Hund's exchange J significantly lowers U_c.

The transition changes from continuous to discontinuous with finite J.

Abstract

Mott metal-insulator transitions in an M-fold orbitally degenerate Hubbard model are studied by means of a generalization of the linearized dynamical mean-field theory. The method allows for an efficient and reliable determination of the critical interaction U_c for any integer filling n and different M at zero temperature. For half-filling a linear dependence of U_c on M is found. Inclusion of the (full) Hund's rule exchange J results in a strong reduction of U_c. The transition turns out to change qualitatively from continuous for J=0 to discontinuous for any finite J.