Phase Diagrams of 4He on Flat and Curved Environments

2013

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We report diffusion Monte Carlo calculations on the phase diagrams of para-H 2 and ortho-D 2 adsorbed on top of a first layer of the same substances on graphene. We found that the ground state of the second layer is a triangular incommensurate solid for both isotopes. The densities for promotion to a second layer and for the onset of a two-dimensional solid on that second layer compare favorably with available experimental data in both cases.

Section: Introductionsupporting

confidence: 80%

Second layer of H2and D2adsorbed on graphene

2013

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“…(1) corresponds to the sum of all individual C-He interactions, modeled by the accurate Carlos and Cole interatomic potential 21 . The graphite sheets containing the carbon atoms were simulated in the same way as in previous literature 18,19,[22][23][24][25] . V (r ij ) stands for the helium-helium Aziz potential 26 , a standard of the theoretical descriptions of helium at low temperatures.…”

mentioning

confidence: 99%

Fluid and registered phases in the second layer ofHe3on graphite

2018

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A quantum Monte Carlo approach, considering all the corrugation effects, was used to calculate the complete phase diagram of the second 3 He layer adsorbed on graphite. We found that a firstlayer triangular solid was in equilibrium with a gas in the second layer. At a surface density 0.166 ± 0.001Å −2 , this fluid changes into two first-layer registered phases: 4/7 and 7/12 solids. The 7/12 arrangement transforms into an incommensurate triangular structure of ρ = 0.189 ± 0.001 A −2 upon further helium loading. A recently proposed hexatic phase was found to be unstable with respect to those commensurate solids.

“…V ext (r) is the total interaction of each helium atom at position r with all the carbon atoms in the graphite substrate. This term is made up of a sum of individual C-He interactions, each of them modeled by the anisotropic Carlos-Cole potential 26,27 , even though no influence of the C-He anisotropy is expected in the behaviour of the second layer, as has been already proved for a second layer of 4 He on the same substrate 27 . As in previous works, the substrate structure was modeled by an stack of honeycomb 2D-lattices separated by 3.35Å in the typical A-B-A-B graphite disposition.…”

Section: Methodsmentioning

confidence: 83%

He3on preplated graphite

2016

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By using the diffusion Monte Carlo method, we obtained the full phase diagram of 3 He on top of graphite preplated with a solid layer of 4 He. All the 4 He atoms of the substrate were explicitly considered and allowed to move during the simulation. We found that the ground state is a liquid of density 0.007 ± 0.001Å −2 , in good agreement with available experimental data. This is significantly different from the case of 3 He on clean graphite, in which both theory and experiment agree on the existence of a gas-liquid transition at low densities. Upon an increase in 3 He density, we predict a first-order phase transition between a dense liquid and a registered 7/12 phase, the 4/7 phase being found metastable in our calculations. At larger second-layer densities, a final transition is produced to an incommensurate triangular phase.