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.
Highlights
Ultracold quantum gases represent excellent test grounds to challenge our understanding of the physics of strongly interacting Fermi systems
For mass imbalances beyond those considered in the present work, it has been observed in the asymmetric 18–21]. For one dimensional (1D) Hubbard model that FFLO-type ordering is eventually suppressed
Studies based on exact diagonalization (ED) explored shot-noise correlations [82] and a related measure [83] to study the influence of mass imbalance on pair formation in harmonically trapped spin-balanced few-body systems have been performed. We address this quantity in the presence of spin imbalance for many-body systems and show that unambiguous features emerge which can potentially be identified in currently available experimental setups
Summary
Ultracold quantum gases represent excellent test grounds to challenge our understanding of the physics of strongly interacting Fermi systems. In addition to the preparation of systems with two different hyperfine states of the same atom species, recent experiments explored the possibility to realize heteronuclear mixtures such as 6Li-40K, 40K-161Dy or 6Li-53Cr, which feature a mass imbalance between the spin-up and spin-down fermions [28,29,30,31] These setups represent a compelling test ground for our picture of the underlying pair formation. Our ultimate goal is to arrive at an experimentally accessible quantity to study pairing in spinand mass-imbalanced systems, and to that end we present numerical results for the so-called shot-noise correlation function as obtained from the CL approach [50,51,52] The latter was recently found to provide a promising way to circumvent the sign problem in nonrelativistic Fermi gases [38,53,54].
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