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

Abstract

Effects of longitudinal (JZ) and transverse (including spin-flip JX and pair-hopping JP 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 JX,P/JZ when JX,P/JZ<1, and has the largest region in the isotropic case (JX,P/JZ=1); and further increasing spin-flip Hund’s coupling to JX,P/JZ>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 JX,P/JZ<1 has less effect on Mott transition, while a large JX,P/JZ>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.