Clustering and phase transitions in a 2D superfluid with immiscible active impurities

TL;DR

This study investigates how impurities affect phase transitions in a 2D quantum superfluid, revealing impurity clustering, its impact on transition temperatures, and the dependence on impurity interactions and volume.

Contribution

It introduces a model combining classical impurities with a quantum fluid to analyze impurity clustering and its effects on superfluid phase transitions.

Findings

Impurities spontaneously cluster during thermalization.

Clustering can break due to thermal fluctuations at certain temperatures.

Impurities increase the condensation transition temperature by up to 20%.

Abstract

Phase transitions of a finite-size two-dimensional quantum fluid of bosons in presence of impurities are studied by using the truncated Gross-Pitaevskii model. Impurities are described with classical degrees of freedom. A spontaneous clustering of impurities during the thermalization is observed. Depending on the interaction among impurities, such clusters can break due to thermal fluctuations at temperatures where the condensed fraction is still significant. Clustering is found to increase the condensation transition temperature. The condensation and the Berezinskii-Kosterlitz-Thouless transition temperatures are determined numerically and found to strongly depend on the volume occupied by the impurities. A relative increase up to a 20% of their respective values is observed, whereas their ratio remains approximately constant.