Pairing patterns in one-dimensional spin- and mass-imbalanced Fermi gases

Abstract

We study spin- and mass-imbalanced mixtures of spin-1/2 fermions interacting via an attractive contact potential in one spatial dimension. Specifically, we address the influence of unequal particle masses on the pair formation by means of the complex Langevin method. By computing the pair-correlation function and the associated pair-momentum distribution we find that inhomogeneous pairing is present for all studied spin polarizations and mass imbalances. To further characterize the pairing behavior, we analyze the density-density correlations in momentum space, the so-called shot noise, which is experimentally accessible through time-of-flight imaging. At finite spin polarization, the latter is known to show distinct maxima at momentum configurations associated with the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) instability. Besides those maxima, we find that additional features emerge in the noise correlations when mass imbalance is increased, revealing the stability of FFLO-type correlations against mass imbalance and furnishing an experimentally accessible signature to probe this type of pairing.

Unconventional pairing in few-fermion systems tuned by external confinement

“…pairing with zero or nonzero net pair momentum) requires a detailed knowledge of the superconducting correlation function. It has been previously shown [27,28,49] that such information can also be obtained from the two-point noise correlation G between the two components, which is directly experimentally accessible from two-body density measurements [50][51][52]. In the momentum domain, the distribution of the noise correlation is given by…”

Low-dimensional fluctuations and pseudogap in Gaudin-Yang Fermi gases

“…However, no one shows how the pseudogap phenomena occur in this famous 1D model. Moreover, the possibility of an inhomogeneous pairing state called Fulde-Ferrel-Larkin-Ovchinikov-(FFLO)-like state [71,72] has also been extensively investigated in a spinimbalanced 1D system [73][74][75][76][77][78][79] since the 1D FFLO-like state is expected to be robust against fluctuations. To see this, a quantitative analysis of fluctuation effects are really desired.…”

Complex Langevin study for polarons in an attractively interacting one-dimensional two-component Fermi gas

“…One interesting application of the complex Langevin method is to study the transition from degenerate Fermi-polaron regime to classical Boltzmann-gas regime of a unitary spinimbalanced Fermi gas which is found to be a sharp transition by a cold-atom experiment using 6 Li Fermi gases in a three-dimensional box potential [61]. Also, it is interesting to explore an inhomogeneous pairing phase [35,36] and in-medium bound states [62], which cannot be addressed by quantum Monte Carlo simulation due to the sign problem in the mass-and population-imbalanced systems. In order to discuss such phenomena, we need more elaborate estimation of systematic errors.…”

“…In the context of cold fermionic atoms, the complex Langevin method is applied to rotating bosons [32], polarized fermions [33][34][35][36], unpolarized fermions with contact repulsive interactions [37] and mass imbalanced fermions [38] to study ground state energy, thermodynamic quantities and Fulde-Ferrell-Larkin-Ovchinnikov-type pairings (see also a recent review [39]).…”