The impurity problem in a bilayer system of dipoles

TL;DR

This paper investigates how a dipolar impurity interacts with a fermionic bilayer system, revealing a crossover from free to tightly-bound polaron states as the interlayer distance decreases, using quantum Monte Carlo simulations.

Contribution

It introduces a detailed quantum Monte Carlo analysis of impurity behavior in a dipolar bilayer, highlighting the polaron crossover in a Wigner crystal regime.

Findings

Effective mass increases significantly at small layer distances.

Binding energy varies with interlayer separation and interaction strength.

Polaron behavior transitions from free to tightly-bound as layers approach.

Abstract

We consider a bilayer geometry where a single impurity moves in a two-dimensional plane and is coupled, via dipolar interactions, to a two-dimensional system of fermions residing in the second layer. Dipoles in both layers point in the same direction oriented by an external field perpendicular to the plane of motion. We use quantum Monte Carlo methods to calculate the binding energy and the effective mass of the impurity at zero temperature as a function of the distance between layers as well as of the in-plane interaction strength. In the regime where the fermionic dipoles form a Wigner crystal, the physics of the impurity can be described in terms of a polaron coupled to the bath of lattice phonons. By reducing the distance between layers this polaron exhibits a crossover from a free-moving to a tightly-bound regime where its effective mass is orders of magnitude larger than the bare mass.