Supersolid Phase with Cold Polar Molecules on a Triangular Lattice

Abstract

We study a system of heteronuclear molecules on a triangular lattice and analyze the potential of this system for the experimental realization of a supersolid phase. The ground state phase diagram contains superfluid, solid and supersolid phases. At finite temperatures and strong interactions there is an additional emulsion region, in contrast to similar models with short-range interactions. We derive the maximal critical temperature Tc and the corresponding entropy S/N = 0.04(1) for supersolidity and find feasible experimental conditions for its realization.PACS numbers: 03.75. Hh, 64.70.Tg, 05.30.Jp Long-range interactions are a key ingredient in many models of strongly correlated electronic systems and frustrated quantum magnets [1]. Magnetic dipolar interactions often occur in materials science and compete with short-range ferromagnetic interactions, which leads to spatially modulated phases [2]. The influence of longrange interactions is currently also attracting a lot of interest in cold atomic and molecular gases: the first signatures of long-range interactions have been observed for magnetic interactions in 52 Cr [3,4], while electric dipole and van der Waals interactions between Rydberg states give rise to intriguing collective phenomena [5]. In addition, there are big experimental efforts towards the realization of quantum degenerate polar molecules [6,7,8], where the permanent dipole moment of the molecules gives rise to a strong and highly tunable electric dipoledipole interaction [9,10,11,12,13].In this Letter, we will concentrate on one intriguing aspect of dipolar systems, namely the possibility to observe a supersolid phase in a single component system. While the interpretation of super-phenomena observed with torsional oscillators in solid 4 He remains a puzzle [14], supersolids might be much easier to realize in lattices. While there exist a number of lattice models of hard-core bosons [15,16,17,18,19,20,21,22], soft-core bosons [23] and quantum spins [24,25] most of these models are hard if not impossible to implement in a material. Systems of cold hetero-nuclear molecules are described by similar Hamiltonians but with longer range dipolar interactions. Here, we demonstrate that they show supersolidity under feasible experimental conditions.We consider bosonic polar molecules in a strong electric field along the z-direction, which induces the dipole moment d z ≤ d; here d denotes the permanent dipole moment of the hetronuclear molecule. The dominant interaction between the polar molecules is then given by the dipole-dipole interaction, where the strength of the dipole interaction can be continuously tuned by the strength of the electric field. In addition, the polar molecules are confined into the xy plane by a (1) around n = 1/3. The phases are a superfluid 'SF', supersolid 'SS' and a commensurate solid at density n = 1/3. With the double line we indicate a transition region of the Spivak-Kivelson bubble type (emulsions) gradually going over to a region of incommensurate, floating solids w...

Collective phenomena in a quasi-two-dimensional system of fermionic polar molecules: Band renormalization and excitons

“…Thus, experiments with polar molecules go beyond quantum simulation of effective theories motivated by electronic systems and aim at exploring a genuinely new domain of many-body quantum behavior, unique to dipolar interactions. Dipolar interactions can be utilized to generate long-range interactions of arbitrary shape using microwave fields [11], simulate exotic spin Hamiltonians [12,13] and are theoretically predicted to give rise to numerous interesting collective phenomena such as roton softening [14][15][16], supersolidity [17][18][19][20][21], p-wave superfluidity [22], emergence of artificial photons [23], bilayer quantum phase transitions [24], multi-layer self-assembled chains [25] for bosonic molecules, dimerization and inter-layer pairing [26,27], spontaneous inter-layer coherence [28], itinerant ferroelectricity [29], anisotropic Fermi liquid theory and anisotropic sound modes [30][31][32][33], fractional quantum Hall effect [34], Wigner crystallization [35], density-wave and striped order [36,37], biaxial nematic phase [38], topological superfluidity [39] and Z 2 topological phase [40], just to mention a few.…”

New frontiers for quantum gases of polar molecules

“…[95] with highly magnetic atoms. Dipolar interactions modify the traditional Hubbard model and can lead to novel phases including supersolid and stripe phases [96,97,98]. In bulk gases of bosonic magnetic atoms, the competition between contact and dipolar interactions has led to the observation of droplets, which are stabilized by quantum fluctuations [99,100].…”

Incommensurability Effects on Dipolar Bosons in Optical Lattices

“…Here, between a superfluid and a crystal phase, Pollet et al [13] identified a supersolid phase as well as a microemulsion as proposed in Ref. [26].…”

“…Concerning a quantum regime, recent studies have pointed out that the supersolid phase can be observed in optical lattices [8,11,12,13]. For example, Pollet et al [13] have studied a complete phase diagram of a two-dimensional system composed of cold polar molecules on a triangular lattice.…”

“…For example, Pollet et al [13] have studied a complete phase diagram of a two-dimensional system composed of cold polar molecules on a triangular lattice. The authors proposed a phase diagram that featured a crystal, a superfluid, and, more important, a supersolid phase.…”