Finding the Elusive Sliding Phase in the Superfluid-Normal Phase Transition Smeared by c-Axis Disorder

We consider a stack of weakly Josephson coupled superfluid layers with c-axis disorder in the form of random superfluid stiffnesses and vortex fugacities in each layer as well as random interlayer coupling strengths. In the absence of disorder this system has a 3D XY type superfluid-normal phase transition as a function of temperature. We develop a functional renormalization group to treat the effects of disorder, and demonstrate that the disorder results in the smearing of the superfluid-normal phase transition via the formation of a Griffiths phase. Remarkably, in the Griffiths phase, the emergent power-law distribution of the interlayer couplings gives rise to a sliding Griffiths superfluid, with a finite stiffness in the a-b direction along the layers, and a vanishing stiffness perpendicular to it

Landau Levels in Strained Optical Lattices

We propose a hexagonal optical lattice system with spatial variations in the hopping matrix elements. Just like in the valley Hall effect in strained Graphene, for atoms near the Dirac points the variations in the hopping matrix elements can be described by a pseudo-magnetic field and result in the formation of Landau levels. We show that the pseudo-magnetic field leads to measurable experimental signatures in momentum resolved Bragg spectroscopy, Bloch oscillations, cyclotron motion, and quantization of in-situ densities. Our proposal can be realized by a slight modification of existing experiments. In contrast to previous methods, pseudo-magnetic fields are realized in a completely static system avoiding common heating effects and therefore opening the door to studying interaction effects in Landau levels with cold atoms.Comment: 5 pages, 3 figure

Equilibrium Contact Angles and Dewetting in Capillaries

In this work, we extend the model of contact angles that we have previously developed for sessile drops on a wetted surface to the case of a meniscus in a capillary. The underlying physics of our model describe the intermolecular forces between the fluid and the surface of the capillary that result in the formation of a thin, non-removable fluid layer that coats the capillary wall. We describe the shape of the meniscus using a Young-Laplace equation and an incompressible, two-phase, CFD calculation, both modified to take into account intermolecular forces using the disjoining pressure model. We find that our numerical solutions of the Young-Laplace equation and equilibrium meniscus shapes obtained by CFD agree well with each other. Furthermore, for capillaries that are sufficiently larger than the thickness of the non-removable film, our numerical solutions agree well with the effective contact angle model that we previously developed for sessile drops. Finally, we observe that it is possible to tune the disjoining pressure model parameters so that the intermolecular forces between the liquid and solid molecules becomes so strong compared to the surface tension that our formula for effective contact angle gives an imaginary solution. We analyze this situation using CFD and find that it corresponds to dewetting, where the bulk liquid detaches from the walls of the capillary leaving behind the non-removable thin liquid film.Comment: 20 pages, 7 figure