Spin 3/2 fermions with attractive interactions in a one-dimensional optical lattice: phase diagrams, entanglement entropy, and the effect of the trap

TL;DR

This paper investigates the phase diagram, entanglement entropy, and effects of trapping in spin 3/2 fermionic cold atoms with attractive interactions in a 1D optical lattice, revealing competition between pairing and molecular superfluid phases.

Contribution

It provides a detailed numerical analysis of phase transitions, entanglement properties, and experimental conditions for observing molecular superfluid phases in spin 3/2 fermions.

Findings

Identification of gapped one-particle excitations and phase separation based on two-particle excitation gaps.

Discovery of a molecular superfluid phase with four-particle bound states.

Analysis of phase transition behavior via entanglement entropy and implications for experimental detection.

Abstract

We study spin 3/2 fermionic cold atoms with attractive interactions confined in a one-dimensional optical lattice. Using numerical techniques, we determine the phase diagram for a generic density. For the chosen parameters, one-particle excitations are gapped and the phase diagram is separated into two regions: one where the two-particle excitation gap is zero, and one where it is finite. In the first region, the two-body pairing fluctuations (BCS) compete with the density ones. In the other one, a molecular superfluid (MS) phase, in which bound-states of four particles form, competes with the density fluctuations. The properties of the transition line between these two regions is studied through the behavior of the entanglement entropy. The physical features of the various phases, comprising leading correlations, Friedel oscillations, and excitation spectra, are presented. To make the connection with experiments, the effect of a harmonic trap is taken into account. In particular, we emphasize the conditions under which the appealing MS phase can be realized, and how the phases could be probed by using the density profiles and the associated structure factor. Lastly, the consequences on the flux quantization of the different nature of the pairing in the BCS and MS phases are studied in a situation where the condensate is in a ring geometry.