Pairing, crystallization and string correlations of mass-imbalanced atomic mixtures in one-dimensional optical lattices

¹ Laboratoire de Physique, CNRS UMR 5672, Ecole Normale Supérieure de Lyon, Université de Lyon 46 Allée d'Italie, Lyon, F-69364, France, EU
² CNR-IMM, Sezione di Bologna - via Gobetti 101, I-40129, Bologna, Italy, EU
³ Dipartimento di Fisica and INFN, Università di Bologna - via Irnerio 46, I-40126, Bologna, Italy, EU
⁴ Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences A-6020 Innsbruck, Austria, EU

^a tommaso.roscilde@ens-lyon.fr

Received: 23 September 2011
Accepted: 29 November 2011

Abstract

We numerically determine the very rich phase diagram of mass-imbalanced binary mixtures of hardcore bosons (or equivalently —fermions, or hardcore Bose/Fermi mixtures) loaded in one-dimensional optical lattices. Focusing on commensurate fillings away from half-filling, we find a strong asymmetry between attractive and repulsive interactions. Attraction is found to always lead to pairing, associated with a spin gap, and to pair crystallization for very strong mass imbalance. In the repulsive case the two atomic components remain instead fully gapless over a large parameter range; only a very strong mass imbalance leads to the opening of a spin gap. The spin-gap phase is the precursor of a crystalline phase occurring for an even stronger mass imbalance. The fundamental asymmetry of the phase diagram is at odds with recent theoretical predictions, and can be tested directly via time-of-flight experiments on trapped cold atoms.