Dipolar Bilayer with Antiparallel Polarization -- a Self-Bound Liquid

TL;DR

This paper explores how antiparallel polarized dipolar bilayers form self-bound liquid states due to inter-layer interactions, analyzing their stability, equation of state, and density fluctuations at zero temperature.

Contribution

It demonstrates that antiparallel dipolar bilayers can form stable, self-bound liquids driven by inter-layer dipole interactions, with detailed analysis of their equation of state and stability conditions.

Findings

Self-bound liquid puddles form without external pressure.

Equilibrium density decreases with increasing layer separation.

System becomes unstable at negative pressure near spinodal point.

Abstract

Dipolar bilayers with antiparallel polarization, i.e. opposite polarization in the two layers, exhibit liquid-like rather than gas-like behavior. In particular, even without external pressure a self-bound liquid puddle of constant density will form. We investigate the symmetric case of two identical layers, corresponding to a two-component Bose system with equal partial densities. The zero-temperature equation of state $E(\rho)/N$, where $\rho$ is the total density, has a minimum, with an equilibrium density that decreases with increasing distance between the layers. The attraction necessary for a self-bound liquid comes from the inter-layer dipole-dipole interaction that leads to a mediated intra-layer attraction. We investigate the regime of negative pressure towards the spinodal instability, where the bilayer is unstable against infinitesimal fluctuations of the total density, conformed by calculations of the speed of sound of total density fluctuations.