Twisted superfluid phase in the extended one-dimensional Bose-Hubbard model

TL;DR

This paper investigates a novel twisted superfluid phase in a one-dimensional extended Bose-Hubbard model, characterized by spontaneous time-reversal symmetry breaking and exponential closing of the excitation gap, revealing complex long-range correlations.

Contribution

It introduces the twisted superfluid phase driven by pair tunneling, demonstrating its properties and phase boundaries using density-matrix renormalization group methods.

Findings

Identification of the twisted superfluid phase with degenerate ground states

Exponential closing of the excitation energy gap

Presence of various phases including supersolid and Mott insulator

Abstract

In one-dimensional systems a twisted superfluid phase is found which is induced by a spontaneous breaking of the time-reversal symmetry. Using the density-matrix renormalization group allows us to show that the excitation energy gap closes exponentially causing a quasi-degenerate ground state. The two degenerate ground states are connected by the time-reversal symmetry which manifests itself in an alternating complex phase of the long-range correlation function. The quantum phase transition to the twisted superfluid is driven by pair tunneling processes in an extended Bose-Hubbard model. The phase boundaries of several other phases are discussed including a supersolid, a pair superfluid, and a pair supersolid phase as well as a highly unconventional Mott insulator with a degenerate ground state and a staggered pair correlation function.