Related papers: Superfluidity of Grain Boundaries in Solid Helium-…
We have observed boundaries between hcp $^4$He crystal grains in equilibrium with liquid $^4$He. We have found that, when emerging at the liquid-solid interface, a grain boundary makes a groove whose dihedral angle $2\theta$ is non-zero.…
We investigate the constraints on the superfluid fraction of an amorphous solid following from an upper bound derived by Leggett. In order to accomplish this, we use as input density profiles generated for amorphous solids in a variety of…
Based on a model of the melting of Grain Boundary (GB), we discuss the possibility of the existence of superheated GB state. A Molecular Dynamics simulation presented here shows that the superheated GB state can realized in the high…
We report new measurements in four cells of the thermal boundary resistance $R$ between copper and $^4$He below but near the superfluid-transition temperature $T_\lambda$. For $10^{-7} \leq t \equiv 1 - T/T_\lambda \leq 10^{-4}$ fits of $R…
The possible superfluid transition of supercooled liquid parahydrogen is investigated by quantum Monte Carlo simulations. The cooling protocol adopted here allows for the investigation of a fluid phase down to a temperature T=0.25 K. No…
More than half a century ago Penrose asked: are the superfluid and solid state of matter mutually exclusive or do there exist "supersolid" materials where the atoms form a regular lattice and simultaneously flow without friction? Recent…
Supersolid helium has a rather low transition temperature and a small critical velocity, compared with liquid helium. These properties could be explained in terms of helium's spectrum structure and quantum jumps involving large momentum…
Exciton bound states in solids between electrons and holes are predicted to form a superfluid at high temperatures. We show that by employing atomically thin crystals such as a pair of adjacent bilayer graphene sheets, equilibrium…
We have considered the dislocation network model for the supersolid state in He-4 crystals. In difference with uniform 2D and 3D systems, the temperature of superfluid transition T_c in the network is much smaller than the degeneracy…
The bound state of a He-3 atom at the interface between coexisting crystalline and superfluid phases of He-4 is studied theoretically by means of first principle Quantum Monte Carlo simulations. We consider both the case of a…
We have measured the pressure dependence of the supersolid fraction by a torsional oscillator technique. Superflow is found from 25.6 bar up to 136.9 bar. The supersolid fraction in the low temperature limit increases from 0.6 % at 25.6 bar…
Structural and superfluid properties of para-Hydrogen clusters of size up to N=40 molecules, are studied at low temperature (0.5 K < T < 4 K) by Path Integral Monte Carlo simulations. The superfluid fraction displays an interesting,…
We discuss the hydrodynamic boundary condition for a superfluid moving tangentially to a rough surface. Specifically, we argue that the scattering of quantum fluctuations off surface roughness affects the nature of the boundary condition,…
We consider the roughening of small angle grain boundaries consisting of arrays of dislocations and found two transitions, corresponding to fluctuations of the dislocations along and perpendicular to the boundaries. The latter contributes…
For solid 4He and solid p-H2, using the flow-energy-minimizing one-body phase function and exact T=0 K Monte Carlo calculations of the local density, we have calculated the phase function, the velocity profile and upper bounds for the…
In light of the race towards macroscale superlubricity of graphitic contacts, the effect of grain boundaries on their frictional properties becomes of central importance. Here, we elucidate the unique frictional mechanisms characterizing…
Superfluidity, liquid flow without friction, is familiar in helium. The first evidence for "supersolidity", its analogue in quantum solids, came from recent torsional oscillator (TO) measurements involving 4-He. At temperatures below 200…
We have examined superfluid properties of $^4$He confined to a nano-porous Gelsil glass that has nanopores 2.5 nm in diameter. The pressure-temperature phase diagram was determined by torsional oscillator, heat capacity and pressure…
The formation of helium cavities in coarse-grained materials produces hardening proportional to the number density and size of the cavities and due to the interaction of dislocations with intragranular helium defects. In nanostructured…
Matter at low temperatures exhibits unusual properties such as superfluidity, superconductivity, Bose-Einstein condensation, and supersolidity. These states display quantum mechanical behaviours at scales much larger than atomic dimensions.…