First-order Bose-Einstein condensation with three-body interacting bosons

TL;DR

This paper predicts a novel first-order Bose-Einstein condensation transition in a trapped bosonic system with both attractive two-body and repulsive three-body interactions, revealing a rich phase diagram with a tri-critical point.

Contribution

It introduces the concept of first-order Bose-Einstein condensation driven by three-body interactions and maps out the associated phase diagram with multiple phases and a tri-critical point.

Findings

First-order phase transition characterized by a jump in condensate fraction.

Existence of a tri-critical point where three phases meet.

Potential observation in spin-polarized tritium atoms.

Abstract

Bose-Einstein condensation, observed in either strongly interacting liquid helium or weakly interacting atomic Bose gases, is widely known to be a second-order phase transition. Here, we predict a first-order Bose-Einstein condensation in a cloud of harmonically trapped bosons interacting with both attractive two-body interaction and repulsive three-body interaction, characterized respectively by an $s$-wave scattering length $a<0$ and a three-body scattering hypervolume $D>0$. It happens when the harmonic trapping potential is weak, so with increasing temperature the system changes from a low-temperature liquid-like quantum droplet to a normal gas, and therefore experiences a first-order liquid-to-gas transition. At large trapping potential, however, the quantum droplet can first turn into a superfluid gas, rendering the condensation transition occurred later from a superfluid gas to a normal gas smooth. We determine a rich phase diagram and show the existence of a tri-critical point, where the three phases - quantum droplet, superfluid gas and normal gas - meet together. We argue that an ensemble of spin-polarized tritium atoms could be a promising candidate to observe the predicted first-order Bose-Einstein condensation, across which the condensate fraction or central condensate density jumps to zero and the surface-mode frequencies diverge.