Spontaneous layer selective Mott phase in the bilayer Hubbard model

TL;DR

This paper investigates a bilayer Hubbard model revealing a spontaneous layer selective Mott phase where one layer becomes insulating while the other remains metallic, with phase transitions driven by electron density and inter-layer hopping.

Contribution

It introduces the concept of a spontaneous layer selective Mott phase in the bilayer Hubbard model and analyzes its stability and transition mechanisms.

Findings

Layer symmetry spontaneously breaks, leading to a layer selective Mott phase.

The LSMP phase persists up to moderate inter-layer hopping.

Fermi surface volume jumps at the LSMP to uniform phase transition.

Abstract

Quantum materials featuring both itinerant and localized degrees of freedom exhibit numerous exotic phases and transitions that deviate from the Ginzburg-Landau paradigm. This work uses the composite operator formalism to examine the bilayer strongly correlated Hubbard model. We observe the spontaneous breaking of layer symmetry, where the electron density in one of the layer reaches half-filling, resulting in a layer selective Mott phase (LSMP). This broken symmetry phase becomes unstable at a critical average electronic density away from half-filling. Furthermore, significant layer differentiation persists up to a moderate inter-layer hopping, beyond which the system abruptly transitions to an layer uniform phase (LUP). In the LSMP phase, the electrons in the two layers are weakly hybridized, resulting in a small Fermi surface. The volume of the Fermi surface jumps at the transition from the LSMP to the uniform phase. We also discuss the physical mechanisms leading to the collapse of the LSMP phase under different perturbations.