Collective phenomena in quasi-two-dimensional fermionic polar molecules: band renormalization and excitons

TL;DR

This paper theoretically investigates the effects of dipolar interactions on the energy bands and excitations in a quasi-two-dimensional fermionic polar molecule system, revealing the presence of anti-bound excitons and their experimental relevance.

Contribution

It introduces a detailed theoretical analysis of band renormalization and excitonic phenomena in fermionic polar molecules using Hartree-Fock methods and explores their experimental signatures.

Findings

Identification of inter-subband excitations and anti-bound excitons.

Excitonic modes dominate the spectral weight in the excitation spectrum.

Excitonic effects are observable at current experimental interaction strengths and temperatures.

Abstract

We theoretically analyze a quasi-two-dimensional system of fermionic polar molecules in a harmonic transverse confining potential. The renormalized energy bands are calculated by solving the Hartree-Fock equation numerically for various trap and dipolar interaction strengths. The inter-subband excitations of the system are studied in the conserving time-dependent Hartree-Fock (TDHF) approximation from the perspective of lattice modulation spectroscopy experiments. We find that the excitation spectrum consists of both inter-subband particle-hole excitation continuums and anti-bound excitons, arising from the anisotropic nature of dipolar interactions. The excitonic modes capture the majority of the spectral weight. We also evaluate the inter-subband transition rates in order to investigate the nature of the excitonic modes and find that they are anti-bound states formed from particle-hole excitations arising from several subbands. Our results indicate that the excitonic effects are present for interaction strengths and temperatures accessible in current experiments with polar molecules.