# Phase separations induced by a trapping potential in one-dimensional fermionic systems as a source of core-shell structures

## TL;DR

This paper explores how trapping potentials induce phase separation in one-dimensional ultracold fermionic gases, leading to diverse core-shell structures influenced by system parameters and phase diagram relations.

## Contribution

It investigates the formation and properties of core-shell structures in trapped fermionic systems, highlighting the influence of trap shape, spin imbalance, and interaction strength on phase separation.

## Key findings

- Core-shell structures can include BCS and FFLO states within harmonic traps.
- Spatial separation of BCS and BEC regimes observed in the system.
- External parameters significantly affect the phase configurations.

## Abstract

Ultracold fermionic gases in optical lattices give a great opportunity for creating different types of novel states. One of them is phase separation induced by a trapping potential between different types of superfluid phases. The core-shell structures, occurring in systems with a trapping potential, are a good example of such separations. The types and the sequences of phases which emerge in such structures can depend on spin-imbalance, shape of the trap and on-site interaction strength. In this work, we investigate the properties of such structures within an attractive Fermi gas loaded in the optical lattice, in the presence of the trapping potential and their relations to the phase diagram of the homogeneous system. Moreover, we show how external and internal parameters of the system and parameters of the trap influence their properties. In particular, we show a possible occurrence of the core-shell structure in a system with a harmonic trap, containing the BCS and FFLO states. Additionally, we find a spatial separation of two superfuild states in the system, one in the BCS limit as well as the other one in the tightly bound local pairs (BEC) regime.