Phase separation in fermionic systems with particle-hole asymmetry

TL;DR

This paper explores the phase diagram of a particle-hole asymmetric Hubbard model with correlated hopping, revealing various phase separation phenomena, incommensurate charge correlations, and a transition to a paired insulator, with potential relevance to incommensurate superconductivity.

Contribution

It provides the exact phase boundaries for a Hubbard model with correlated hopping and particle-hole asymmetry, highlighting novel phase separation and incommensurate charge order phenomena.

Findings

Ground state separates into hole and electron conducting phases.

Charge-charge correlations become incommensurate.

Transition to a paired insulator at negative U.

Abstract

We determine the ground-state phase-diagram of a Hubbard Hamiltonian with correlated hopping, which is asymmetric under particle-hole transform. By lowering the repulsive Coulomb interaction U at appropriate filling and interaction parameters, the ground state separates into a hole and an electron conducting phases: two different wave vectors characterize the system and charge-charge correlations become incommensurate. By further decreasing U another transition occurs at which the hole conducting region becomes insulating, and conventional phase separation takes place. Finally, for negative U the whole system eventually becomes a paired insulator. It is speculated that such behavior could be at the origin of the incommensurate superconducting phase recently discovered in the 1D Hirsch model. The exact phase boundaries are calculated in one dimension.