Competing roles of longitudinal and transverse Hund's terms on Mott transitions

摘要

Effects of longitudinal (Jz) and transverse (including spin-flip J(X) and pair-hopping J(p) terms) Hund's couplings on Mott transitions of two-orbital Hubbard models are studied by the rotationally invariant slave boson approach. We show that in the half-filled asymmetric systems, the orbital selective Mott phase (OSMP) expands with increasing J(X,P)/J(z) when J(X,P)/J(Z) < 1, and has the largest region in the isotropic case (J(X,P)/J(Z) = 1); and further increasing spin-flip Hund's coupling to J(X,P)/J(Z) > 1 may quickly suppress the OSMP state. In other near-half-filled systems, the transverse Hund's coupling favors or unfavors the OSMP state, depending on the electronic correlation strength of the systems. In the quarter filled and around systems, a small J(X,P)/J(Z) < 1 has less effect on Mott transition, while a large J(X,P)/J(Z) > 1 enhances the electron itineracy and considerably increases the critical correlation strength of the Mott transition both in symmetric and asymmetric systems. These results could be addressed by different spin-orbital states favored by Jx, jp and Jz components, respectively; and the competing longitudinal and transverse Hund's coupling terms lead to most strong quantum fluctuations in the isotropic system. (C) 2016 Elsevier Inc. All rights reserved.