Suppressed Solitonic Cascade in Spin-Imbalanced Superfluid Fermi Gas

Abstract

Cold atoms experiments offer invaluable information on superfluid dynamics, including decay cascades of topological defects. While the cascade properties are well established for Bose systems, our understanding of their behavior in Fermi counterparts is very limited, in particular in spin-imbalanced systems, where superfluid (paired) and normal (unpaired) particles naturally coexist giving rise to complex spatial structure of the atomic cloud. Here we show, based on a newly developed microscopic approach, that the decay cascades of topological defects are dramatically modified by the spin polarization. We demonstrate that decay cascades end up at different stages: "dark soliton," "vortex ring," or "vortex line," depending on the polarization. We reveal that it is caused by sucking of unpaired particles into the soliton's internal structure. As a consequence vortex reconnections are hindered and we anticipate that quantum turbulence phenomenon can be significantly affected, indicating new physics induced by polarization effects.

Spin-polarized droplets in the unitary Fermi gas

“…Spin reversed components of quasiparticle wavefunctions can be obtained via symmetry relation u n,↑ → v * n,↑ , v n,↓ → u * n,↓ and E n → −E n . The framework has been extensively tested over last years, and it proved to provide an accurate description of various dynamical properties of the strongly interacting Fermi gas, including generation and proliferation of quantum vortices [23] or dynamics of solitonic cascades [15,24]. More details related to technical aspects of solving TDASLDA equations we provide in the Appendix A.…”

Time‐Dependent Density Functional Theory for Fermionic Superfluids: From Cold Atomic Gases − To Nuclei and Neutron Stars Crust

“…Recently, Magierski et al reported on a somewhat related physical system. In polarized systems, one can create unexpectedly stable spatially localized spin polarized droplets, with a similar change in the phase of the pairing gap across the boundary of these droplets …”

Vortex lattice in spin-imbalanced unitary Fermi gas

“…Equation ( 7) was solved self-consistently, and the Broyden algorithm was applied to improve the convergence rate [55,56]. The calculations were executed with the use of W-SLDA Toolkit [36,38,57].…”

“…This property significantly limits the possible forms of an energy density functional (EDF), and it allows for the successful formulation of the DFT framework for the UFG-the approach being in principle exact; see for a review [33]. The framework has been already applied for studies of quantum vortices [34][35][36][37], revealing a remarkable agreement with experiment [38]. Also, it admits the development of the FFLO state at unitarity [39].…”