We investigate superfluid pairing in a two-dimensional Rashba spin-orbit-coupled Fermi gas subject to spin-selective one-body loss. Within the non-Hermitian mean-field framework, we self- consistently solve the gap and number equations and find that moderate dissipation can significantly enhance the pairing gap, resulting in a pronounced nonmonotonic dependence on the dissipation strength. Dissipation also provides an additional control parameter for driving the system across the BCS-BEC crossover. We further analyze the quasi-particle spectrum and identify two distinct superfluid regimes characterized by one and three exceptional rings, separated by an exceptional spectral transition. Interestingly, dissipation can enhance both pairing channels while simultaneously inducing a momentum-dependent phase twist in the triplet component. These results demonstrate that spin-selective dissipation provides a versatile non-Hermitian control knob for manipulating superfluid pairing, spectral structure, and crossover physics in spin-orbit-coupled quantum gases.
We investigate superfluid pairing in a two-dimensional Rashba spin-orbit-coupled Fermi gas subject to spin-selective one-body loss. Within the non-Hermitian mean-field framework, we self- consistently solve the gap and number equations and find that moderate dissipation can significantly enhance the pairing gap, resulting in a pronounced nonmonotonic dependence on the dissipation strength. Dissipation also provides an additional control parameter for driving the system across the BCS-BEC crossover. We further analyze the quasi-particle spectrum and identify two distinct superfluid regimes characterized by one and three exceptional rings, separated by an exceptional spectral transition. Interestingly, dissipation can enhance both pairing channels while simultaneously inducing a momentum-dependent phase twist in the triplet component. These results demonstrate that spin-selective dissipation provides a versatile non-Hermitian control knob for manipulating superfluid pairing, spectral structure, and crossover physics in spin-orbit-coupled quantum gases.
The experimental realizations of artificial spin-orbit coupling (SOC) and non-Hermitian potentials in ultracold atoms provide a versatile platform for exploring their interplay in quantum many-body systems. Here, we investigate a two-component Fermi gas in a three-dimensional cubic lattice with Rashba SOC and a complex-valued interaction arising from two-body loss. Based on a non-Hermitian mean-field theory, this work elucidates the interplay of dissipation and SOC in the pairing behavior of Fermi gases. Dissipation not only drives a phase transition from a superfluid to a normal state and induces a reentrant superfluid but also, synergistically with SOC, significantly expands the stability regions of both the normal and metastable superfluid phases. Moreover, the introduction of a Zeeman field can drive the system into a topological superfluid phase characterized by a nontrivial topological invariant. These results thereby uncover a rich spectrum of pairing phenomena in this dissipative quantum system.
The experimental advances in realizing artificial spin-orbit coupling (SOC) and non-Hermitian potentials in ultracold atomic system open a new avenue for exploring their significant roles in quantum many-body physics. Here, we investigate a non-Hermitian, two-component Fermi system in a cubic lattice with Rashba SOC and complex-valued interaction arising from two-body loss. We adopt the non-Hermitian mean field theory and map out the phase diagram at zero temperature. The interplay of dissipation and on-site interaction drives a dissipation-induced phase transition from superfluid (SF) to normal phase (N). Notably, for weak interaction strengths, this leads to a reentrance of the superfluid state. The presence of SOC significantly expands the parameter regime for both the normal phase and the metastable superfluid phase(MSF). Whereas, the Zeeman field can drive the system from a conventional superfluid into a topological superfluid phase(TSF), characterized by a nontrivial topological invariant. These results enrich our knowledge of pairing superfluidity in Fermi systems.
The recent experimental realization of spin-orbit coupling for ultracold atoms has generated much interest in the physics of spin-orbit-coupled degenerate Fermi gases. Although recently the BCS-BEC crossover in three-dimensional (3D) spin-orbit-coupled Fermi gases has been intensively studied, the corresponding two-dimensional (2D) crossover physics has remained unexplored. In this paper, we investigate, both numerically and analytically, the BCS-BEC crossover physics in 2D degenerate Fermi gases in the presence of the Rashba type of spin-orbit coupling. We derive the mean-field gap and atom-number equations suitable for 2D spin-orbit-coupled Fermi gases and solve them numerically and self-consistently, from which the dependence of the ground-state properties (chemical potential, superfluid pairing gap, ground-state energy per atom) on the system parameters (e.g., binding energy, spin-orbit-coupling strength) is obtained. Furthermore, we derive analytical expressions for these ground-state quantities, which agree well with our numerical results within a broad parameter region. Such analytical expressions also agree qualitatively with previous numerical results for 3D spin-orbit-coupled Fermi gases, where analytical results are lacking. We show that, with increasing spin-orbit coupling (SOC) strength, the chemical potential is shifted by a constant determined by the SOC strength. The superfluid pairing gap is enhanced significantly in the BCS limit for strong SOC, but increases only slightly in the BEC limit.
Motivated by the prospect of realizing a Fermi gas with a synthetic non-Abelian gauge field, we investigate theoretically a strongly interacting Fermi gas in the presence of a Rashba spin-orbit coupling. As the twofold spin degeneracy is lifted by spin-orbit interaction, bound pairs with mixed singlet and triplet components emerge, leading to an anisotropic superfluid. We calculate the relevant physical quantities, such as the momentum distribution, the single-particle spectral function, and the spin structure factor, that characterize the system.
Abstract The equal Rashba-Dresselhaus (ERD) spin-orbit coupling, as the first type to be implemented in cold atom experiments, provides a unique platform for exploring topological quantum phases. This work investigates the ground state of a two-dimensional Fermi gas featuring both ERD coupling and a Zeeman field, mapping out its topological phase diagram throughout the BCS-BEC crossover. We classify the homogeneous superfluid phases into topologically trivial gapped or nontrivial gapless phase based on the nodal structure of the quasiparticle excitation spectrum. We reveal the evolution of topological superfluid states under various conditions by systematically characterizing the phase distribution across key parameters including the spin-orbit coupling strength, two-body binding energy, Zeeman field, and chemical potential. Our findings indicate that spin-orbit coupling enhances triplet pairing and stabilizes the gapless superfluid phase. Moreover, small binding energy, and strong Zeeman field are found to promote the emergence of the gapless phase, particularly the US-II phase identified in this work. These results elucidate the phase transition mechanisms in low-dimensional quantum systems.
The two-body loss associated with inelastic interactions between fermions plays a significant role in realistic many-body systems. Here we study a two-component non-Hermitian Bardeen-Cooper-Schrieffer superfluidity with spin imbalance and two-body loss characterized by a complex-valued s-wave interaction in a square lattice. At the mean-field level, we map out the zero-temperature phase diagram and observe a dissipation-induced transition from superfluid to normal phase as well as a distinctive revival of the superfluid state in the weakly interacting regime applicable to both spin-balanced and spin-imbalanced systems. In the spin-imbalanced case, we find that the effective density of states involving weight functions reduces the regions in k space contributing to pairing, hence leading to a pronounced expansion of the normal phase on the phase diagram. Additionally, we analyze the order parameter, condensate energy, quasiparticle spectra, momentum distribution, and compressibility to characterize the presenting phases and phase transitions.