Coexistence of phase transitions and hysteresis near BEC

TL;DR

This paper investigates phase transitions and hysteresis phenomena near Bose-Einstein condensation in a Bose gas with finite-range interactions, revealing complex multivalued behaviors and the persistence of hysteresis under strong interactions.

Contribution

It provides a unified theoretical framework to analyze phase transitions and hysteresis near BEC, incorporating recent methods to eliminate self-interaction in the T-matrix approximation.

Findings

First-order phase transition indicators near BEC onset.

Multivalued equation of state near the transition.

Hysteresis persists at strong interactions.

Abstract

Multiple phases occurring in a Bose gas with finite-range interaction are investigated. In the vicinity of the onset of Bose-Einstein condensation (BEC) the chemical potential and the pressure show a van-der-Waals like behavior indicating a first-order phase transition although there is no long-range attraction. Furthermore the equation of state becomes multivalued near the BEC transition. For a Hartree-Fock or Popov (Hartree-Fock-Bogoliubov) approximation such a multivalued region can be avoided by the Maxwell construction. For sufficiently weak interaction the multivalued region can also be removed using a many-body \mbox{T-matrix} approximation. However, for strong interactions there remains a multivalued region even for the \mbox{T-matrix} approximation and after the Maxwell construction, what is interpreted as a density hysteresis. This unified treatment of normal and condensed phases becomes possible due to the recently found scheme to eliminate self-interaction in the \mbox{T-matrix} approximation, which allows to calculate properties below and above the critical temperature.