Modulated pair condensate of p-orbital ultracold fermions

TL;DR

This paper predicts a novel $p$-orbital pair condensate in spin-imbalanced ultracold fermions within optical lattices, characterized by finite momentum pairing and potential experimental detection, expanding understanding of unconventional superfluid phases.

Contribution

It introduces the concept of a $p$-orbital pair condensate with finite momentum in spin-imbalanced Fermi gases, supported by DMRG and mean-field analysis, and explores its phase diagram and experimental signatures.

Findings

Finite momentum $p$-orbital pairing identified.

Phase diagram shows wide filling range for condensate.

Unconventional BEC beyond Feynman's no-node theorem.

Abstract

We show that an interesting of pairing occurs for spin-imbalanced Fermi gases under a specific experimental condition---the spin up and spin down Fermi levels lying within the $p_x$ and $s$ orbital bands of an optical lattice, respectively. The pairs condense at a finite momentum equal to the sum of the two Fermi momenta of spin up and spin down fermions and form a $p$-orbital pair condensate. This $2k_F$ momentum dependence has been seen before in the spin- and charge- density waves, but it differs from the usual $p$-wave superfluids such as $^3$He, where the orbital symmetry refers to the relative motion within each pair. Our conclusion is based on the density matrix renormalization group analysis for the one-dimensional (1D) system and mean-field theory for the quasi-1D system. The phase diagram of the quasi-1D system is calculated, showing that the $p$-orbital pair condensate occurs in a wide range of fillings. In the strongly attractive limit, the system realizes an unconventional BEC beyond Feynman's no-node theorem. The possible experimental signatures of this phase in molecule projection experiment are discussed.