Browsing by Author "Cinti, Fabio"
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- ItemClassical and quantum filaments in the ground state of trapped dipolar Bose gases(American Physical Society, 2017) Cinti, Fabio; Boninsegni, MassimoWe study, by quantum Monte Carlo simulations, the ground state of a harmonically confined dipolar Bose gas with aligned dipole moments and with the inclusion of a repulsive two-body potential of varying range. Two different limits can clearly be identified, namely, a classical one in which the attractive part of the dipolar interaction dominates and the system forms an ordered array of parallel filaments and a quantum-mechanical one, wherein filaments are destabilized by zero-point motion, and eventually the ground state becomes a uniform cloud. The physical character of the system smoothly evolves from classical to quantum mechanical as the range of the repulsive two-body potential increases. An intermediate regime is observed in which ordered filaments are still present, albeit forming different structures from the ones predicted classically; quantum-mechanical exchanges of indistinguishable particles across different filaments allow phase coherence to be established, underlying a global superfluid response.
- ItemExchange-induced crystallization of soft-core bosons(Institute of Physics, 2014-03-28) Cinti, Fabio; Boninsegni, Massimo; Pohl, ThomasWe study the phase diagram of a two-dimensional assembly of bosons interacting via a soft-core repulsive pair potential of varying strength, and compare it to that of the equivalent system in which particles are regarded as distinguishable. We show that quantum-mechanical exchanges stabilize a ‘cluster crystal’ phase in a wider region of parameter space than predicted by calculations in which exchanges are neglected. This physical effect is diametrically opposite to that which takes place in hard-core Bose systems such as 4He, wherein exchanges strengthen the fluid phase. This is underlain in the cluster crystal phase of soft-core bosons by the free energy gain associated with the formation of local Bose–Einstein condensates.
- ItemGlass transitions in monodisperse cluster-forming ensembles : vortex matter in type-1.5 superconductors(American Physical Society, 2017) Diaz-Mendez, Rogelio; Mezzacapo, Fabio; Lechner, Wolfgang; Cinti, Fabio; Babaev, Egor; Pupillo, GuidoAt low enough temperatures and high densities, the equilibrium configuration of an ensemble of ultrasoft particles is a self-assembled, ordered, cluster crystal. In the present Letter, we explore the out-of-equilibrium dynamics for a two-dimensional realization, which is relevant to superconducting materials with multiscale intervortex forces. We find that, for small temperatures following a quench, the suppression of the thermally activated particle hopping hinders the ordering. This results in a glass transition for a monodispersed ensemble, for which we derive a microscopic explanation in terms of an “effective polydispersity” induced by multiscale interactions. This demonstrates that a vortex glass can form in clean systems of thin films of “type-1.5” superconductors. An additional setup to study this physics can be layered superconducting systems, where the shape of the effective vortex-vortex interactions can be engineered.
- ItemPhases of dipolar bosons in a bilayer geometry(American Physical Society, 2017) Cinti, Fabio; Wang, Daw-Wei; Boninsegni, MassimoWe study, by first-principles computer simulations, the low-temperature phase diagram of bosonic dipolar gases in a bilayer geometry as a function of the two control parameters, i.e., the in-plane density and the interlayer distance.We observe four distinct phases, namely, paired and decoupled superfluids, as well as a crystal of dimers and one consisting of two aligned crystalline layers. A direct quantum phase transition from a dimer crystal to two independent superfluids is observed in a relatively wide range of parameters. No supersolid phase is predicted for this system.
- ItemSuperfluid filaments of dipolar bosons in free space(American Physical Society, 2017) Cinti, Fabio; Cappellaro, Alberto; Salasnich, Luca; Macri, TommasoWe systematically investigate the zero temperature phase diagram of bosons interacting via dipolar interactions in three dimensions in free space via path integral Monte Carlo simulations with a few hundreds of particles and periodic boundary conditions based on the worm algorithm. Upon increasing the strength of the dipolar interaction and at sufficiently high densities we find a wide region where filaments are stabilized along the direction of the external field. Most interestingly by computing the superfluid fraction we conclude that the superfluidity is anisotropic and is greatly suppressed along the orthogonal plane. Finally, we perform simulations at finite temperature confirming the stability of the filaments against thermal fluctuations and provide an estimate of the superfluid fraction in the weak coupling limit in the framework of the Landau two-fluid model.