Ground-State Ferromagnetic Transition in Strongly Repulsive One-Dimensional Fermi Gases

TL;DR

This paper proves that in a one-dimensional Fermi gas, the ground state transitions from singlet to ferromagnetic as interactions change from repulsive to attractive, with implications for experimental observations of spin states.

Contribution

The authors establish a rigorous theoretical framework showing the ground state transition and analyze the effects of symmetry breaking fields on spin states in 1D Fermi gases.

Findings

Ground state shifts from singlet to ferromagnetic during interaction change

Exact calculations demonstrate phase separation and spin segregation

Quantum wavefunction exhibits phase separation in the system

Abstract

We prove that as a one-dimensional Fermi gas is brought across the resonance adiabatically from large repulsion to large attraction, the singlet ground state will give way to the maximum spin state, which is the lowest energy state among the states accessible to the system in this process. In the presence of tiny symmetry breaking fields that destroy spin conservation, the singlet ground state can evolve to the ferromagnetic state or a spin segregated state. We have demonstrated these effects by exact calculations on fermion cluster relevant to current experiments, and have worked out the quantum mechanical wavefunction that exhibits phase separation.