Complex and real unconventional Bose-Einstein condensations in high orbital bands

TL;DR

This paper provides a theoretical analysis of unconventional Bose-Einstein condensates in high orbital bands, revealing complex and real-valued states with nodal structures, driven by a quantum phase transition, and exhibiting vortex-antivortex lattice patterns.

Contribution

It introduces a theoretical framework for understanding complex and real UBECs in high bands, highlighting their nodal structures and symmetry-breaking properties.

Findings

UBECs characterized by complex wavefunctions with nodal points.

Quantum phase transition driven by band and interaction energy competition.

Spontaneous breaking of time-reversal symmetry with vortex-antivortex lattice formation.

Abstract

We perform the theoretical study on the unconventional Bose-Einstein condensations (UBEC) in the high bands of optical lattices observed by Hemmerich's group. These exotic states are characterized by complex-valued condensate wavefunctions with nodal points, or real-valued ones with nodal lines, thus are beyond the {\it "no-node"} paradigm of the conventional BECs. A quantum phase transition is driven by the competition between the single particle band and interaction energies. The complex UBECs spontaneously break time-reversal symmetry, exhibiting a vortex-antivortex lattice structure.