Topological quantum phase transition in the BEC-BCS crossover phenomena

TL;DR

This paper investigates a topological quantum phase transition in the BEC-BCS crossover, revealing a transition characterized by a change in topological invariants without bulk gap closing.

Contribution

It introduces a topological perspective to the BEC-BCS crossover using a local Z_2 Berry phase, identifying a quantum phase transition without gap closing.

Findings

Topological quantum phase transition identified in BEC-BCS crossover

Transition characterized by local Z_2 Berry phase

No bulk gap closing during the transition

Abstract

A crossover between the Bose Einstein condensation (BEC) and BCS superconducting state is described topologically in the chiral symmetric fermion system with attractive interaction. Using a local Z_2 Berry phase, we found a quantum phase transition between the BEC and BCS phases without accompanying the bulk gap closing.