Color superfluidity of neutral ultracold fermions in the presence of color-flip and color-orbit fields

Abstract

We describe how color superfluidity is modified in the presence of color-flip and color-orbit fields in the context of ultra-cold atoms, and discuss connections between this problem and that of color superconductivity in quantum chromodynamics. We study the case of s-wave contact interactions between different colors, and we identify several superfluid phases, with five being nodal and one being fully gapped. When our system is described in a mixed color basis, the superfluid order parameter tensor is characterized by six independent components with explicit momentum dependence induced by color-orbit coupling. The nodal superfluid phases are topological in nature, and the low temperature phase diagram of color-flip field versus interaction parameter exhibits a pentacritical point, where all five nodal color superfluid phases converge. These results are in sharp contrast to the case of zero color-flip and color-orbit fields, where the system has perfect U(3) symmetry and possesses a superfluid phase that is characterized by fully gapped quasiparticle excitations with a single complex order parameter with no momentum dependence and by inert unpaired fermions representing a non-superfluid component. In the latter case, just a crossover between a Bardeen-Cooper-Schrieffer and a Bose-Einstein-Condensation superfluid occurs. Furthermore, we analyse the order parameter tensor in a total pseudo-spin basis, investigate its momentum dependence in the singlet, triplet and quintet sectors, and compare the results with the simpler case of spin-1/2 fermions in the presence of spin-flip and spin-orbit fields, where only singlet and triplet channels arise. Finally, we analyse in detail spectroscopic properties of color superfluids in the presence of color-flip and color-orbit fields, such as the quasiparticle excitation spectrum, momentum distribution, and density of states to help characterize all the encountered topological quantum phases, which can be realized in fermionic isotopes of Lithium, Potassium and Ytterbium atoms with three internal states trapped.

Emergent QCD Kondo effect in two-flavor color superconducting phase

“…Although the 2SC Kondo effect does not necessarily need dynamical gluon exchanges, which can be substituted by contact interactions, a non-Abelian matrix on each interaction vertex is an indispensable ingredient. While Cooper pairing with a "color-flipping" effect was recently discussed [54], a noncommutative property is yet more demanding. Nevertheless, the direction for ultracold atoms deserves further study.…”

Eigenspectrum, Chern Numbers and Phase Diagrams of Ultracold Color-orbit Coupled SU(3) Fermions in Optical Lattices

“…These techniques can also be applied to SU(3) fermions with three internal states (colors) and allow for the investigation of exotic topological insulating phases that arise in optical lattices when artificial magnetic, color-orbit and color-flip fields are varied. The present system in optical lattices expands the realm of phases beyond Fermi liquid and superfluid for SU (3) fermions in the presence of color-orbit and color-flip fields analyzed in the continuum or in harmonic traps [40,41].…”

Superfluid transition temperature and fluctuation theory of spin-orbit and Rabi coupled fermions with tunable interactions

“…These systems are intriguing both because they reflect physics studied extensively in the context of semiconductors [30,31], and because they provide a platform for realizing tunable non-Abelian fields in the laboratory. Thus, while the holy grail of a full optical simulation of QCD remains years in the future, there do exist notable analogies between quark matter and cold atomic systems (e.g., non-Abelian fields, evolution between strongly and weakly coupled limits) within near-term experimental reach [32][33][34][35]. Investigations of spin-orbit coupled ultracold gases have also included optical lattices [36][37][38][39][40][41][42][43][44][45], thus enlarging the number of possible physical systems that can be accessible experimentally.…”