Unconventional pairing in one-dimensional systems of a few mass-imbalanced ultracold fermions

TL;DR

This paper investigates unconventional pairing phenomena in a few-body one-dimensional ultracold fermionic system with mass imbalance, revealing conditions for coexistence of different pairing mechanisms and potential experimental signatures.

Contribution

It provides an exact diagonalization analysis showing how mass imbalance influences pairing types and phase coexistence in few-body ultracold fermionic systems.

Findings

Conventional pairs dominate at small mass imbalance.

Large mass ratios favor unconventional pairing and FFLO phase.

Coexistence of pairing mechanisms possible at moderate mass ratios.

Abstract

We study the ground-state properties of a two-component fermionic mixture effectively confined in a one-dimensional harmonic trap. We consider scenarios when numbers of particles in components are the same but particles have different masses. We examine whether it is possible to detect signatures of an unconventional pairing between opposite-spin fermions in the presence of attractive interactions. For this purpose, we perform the exact diagonalization of the many-body Hamiltonian and study the two-particle reduced density matrix. In agreement with expectations, we confirm that the many-body ground state is dominated by conventional pairs with a negligible total momentum for a small mass imbalance. Furthermore, we show that for sufficiently large mass ratios the domination of fundamentally different pairs is established and the Fulde-Ferrell-Larkin-Ovchinnikov phase is supported. Finally, we argue that the two mechanisms can coexist in the regime of moderate mass ratios. Due to the current experimental progress in obtaining ultra-cold fermionic systems in a few-body regime, our predictions may have some importance for the upcoming experiments.