Quantum Transition to Supersolid Phase

Giulio Biagioni, Nicolò Antolini, Aitor Alaña +5 more

Supersolids are a fundamental quantum phase of matter where the global phase and translational symmetries are spontaneously broken.The recently discovered supersolidity in quantum gases of strongly magnetic atoms gives the opportunity to explore in depth how superfluidity and crystalline order are mixed in this fascinating phase.The dipolar supersolid is usually created from a Bose-Einstein condensate, i.e., a standard superfluid, crossing a quantum phase transition that is related to the crystallization transitions of ordinary matter.In this work, we assess experimentally and theoretically the character of the superfluidsupersolid quantum phase transition.We find that one-row supersolids can have already two types of phase transitions, discontinuous and continuous, that are reminiscent of the first-and second-order transitions predicted in the thermodynamic limit in 2D and 1D, respectively.The dimensional crossover is peculiar to supersolids, is controlled via the transverse confinement and the atom number, and can be justified on the general ground of the Landau theory of phase transitions.The quasiadiabatic crossing of a continuous phase transition opens new directions of investigation for supersolids.

Tie-Fu Zhang, Wei Han, Renyuan Liao +2 more

S. Balibar

Chia-Min Chung, Shiang Fang, Pochung Chen

We investigate two-species bosons in a two-dimensional square lattice by the quantum Monte Carlo method. We show that the interspecies attraction and nearest-neighbor intraspecies repulsion result in the pair-supersolid phase, where a diagonal solid order coexists with an off-diagonal pair-superfluid order. The quantum and thermal transitions out of the pair-supersolid phase are characterized. It is found that there is a direct first-order transition from the pair-supersolid phase to the double-superfluid phase without an intermediate region. Furthermore, the melting of the pair supersolid occurs in two steps. Upon heating, first the pair superfluid is destroyed via a Kosterlitz-Thouless transition, then the solid order melts via an Ising transition.

Simone Montangero

P. B. Blakie, Lauriane Chomaz, D. Baillie +1 more

We investigate the excitation spectrum and compressibility of a dipolar Bose-Einstein condensate in an infinite tube potential in the parameter regime where the transition between superfluid and supersolid phases occurs. Our study focuses on the density range in which crystalline order develops continuously across the transition. Above the transition the superfluid shows a single gapless excitation band, phononic at small momenta and with a roton at a finite momentum. Below the transition, two gapless excitations branches (three at the transition point) emerge in the supersolid. We examine the two gapless excitation bands and their associated speeds of sound in the supersolid phase. Our results show that the speeds of sound and the compressibility are discontinuous at the transition, indicating a second-order phase transition. These results provide valuable insights into the identification of supersolid phenomena in dipolar quantum gases and the relationship to supersolidity in spin-orbit coupled gases.