Structure and superfluidity of He4 films on plated graphite

Nyéki, J.; Ray, Rajyavardhan; Sheshin, G. A.; Maı̆danov, V. A.; Mikheev, V. A.; Cowan, Brian; Saunders, J.

doi:10.1063/1.593382

Cited by 10 publications

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“…Vertical dashed lines show layer promotions, as determined by compressibility minima obtained from vapor pressure isotherms[9].FIG. 4.…”

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“…The oscillator operates at 1056 Hz and its motion is driven and detected capacitatively. Further experimental details and a preliminary account of some of the results are given elsewhere [9].The bilayer and trilayer HD preplating films are defined by vapor pressure isotherms at 12 and 10 K. Two HD layers correspond to 46.05 STP cm 3 and three layers to 66.22 STP cm 3 for our substrate, while point B of a 4 He vapor pressure isotherm at 4.2 K corresponds to 27.4 STP cm 3 . Since these data scale very well with neutron scattering measurements of the densities of solid helium and hydrogen films [10], we are confident that the chosen preplating coverages are close to exactly two and three layers, providing a well characterized surface for adsorption of 4 He.…”

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Superfluidity of Atomically LayeredH4eFilms

et al. 1998

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The superfluidity of 4 He films adsorbed on the atomically flat surface of graphite, preplated with HD to tune the surface binding potential, has been studied using a torsional oscillator. The superfluidity of a single uniform fluid layer of 4 He shows an intrinsic coverage dependent suppression, while the fluid bilayer is fully superfluid at T 0. The contribution of nonvortex excitations in the film to the normal density shows a strong dependence on coverage, arising from the atomic layering of the film.[S0031-9007 (98)06517-X] PACS numbers: 67.70. + n, 67.40.Db, 67.40.Kh A thin 4 He film on a planar substrate is a paradigm two dimensional Bose system. It is predicted to undergo a superfluid phase transition due to the unbinding of vortex-antivortex pairs [1], with a discontinuous jump in the superfluid density obeying a universal scaling relation with the transition temperature [2]; r s ͑T c ͒͞T c 2m 2 k B ͞ph 2 . This was first verified by torsional oscillator studies of films adsorbed on a Mylar sheet [3].Since such an atomically rough substrate provides a heterogeneous binding potential for the adsorbed 4 He atoms, there is a threshold coverage, referred to as the "inert" layer, before superfluidity is observed. The simplest picture is that an amorphous solid 4 He coating of the surface is required in order to screen the disordered substrate potential, before subsequent 4 He atoms are delocalized and can undergo a superfluid transition [4].More recently there has been renewed interest in films adsorbed on the atomically flat surface of graphite, which provides an essentially uniform binding potential, resulting in a 4 He film that, by contrast, displays distinct atomic layering. Evidence for such layering comes from vapor pressure isotherms [5], heat capacity [6], and third sound measurements [5], as well as first principles calculations of the film structure [7]. This layered structure influences the development of superfluidity in the film, as first shown by Crowell and Reppy [8].This Letter discusses (i) the superfluidity of a fluid monolayer, (ii) the properties of a superfluid bilayer, and (iii) the dependence of the nonvortex excitations in the film on its structure. We have made a systematic investigation of the effect of tuning the substrate potential by preplating the graphite surface with hydrogen deuteride (HD) on the superfluid response. The number of solid 4 He layers that can form is reduced to one for a bilayer [5] or trilayer preplating, and zero for the thick preplating film we have investigated. By contrast, two 4 He layers will solidify on bare graphite. In these systems we are able to study the superfluid transition for a single fluid layer, which for the thick preplating corresponds to "submonolayer superfluidity." For all three preplatings we find 2D condensation for fluid coverages ,3.5 nm 22 and clear evidence at higher densities for a coverage dependent suppression of superfluidity in the uniform fluid layer. This latter effect is quite distinct from the "inert layer" found on hetero...

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“…Vertical dashed lines show layer promotions, as determined by compressibility minima obtained from vapor pressure isotherms[9].FIG. 4.…”

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Superfluidity of Atomically LayeredH4eFilms

et al. 1998

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“…These experiments rely on precise torsional oscillator techniques to measure the superfluid response. For the application of this method to the study of 4 He on graphite, see [24][25][26].…”

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Atomically Layered Helium Films at Ultralow Temperatures: Model Systems for Realizing Quantum Materials

2020

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“…The problem of 4 He atoms deposited on solid substrates has been identified for many decades as a bosonic many-body problem that could exhibit a rich phase diagram including the possibility of dimensional crossover [1][2][3][4][5][6][7][8]. Graphite was first recognized as an ideal twodimensional substrate due to its exceptional homogeneity, [9] and extensive experimental [10,11] and theoretical studies [12][13][14] have demonstrated that under the right circumstances a superfluid He film can develop on the graphite surface. Because 4 He atoms are neutral, the many-body interactions that determine the behavior of this system are the van der Waals (VDW) interactions between He atom pairs and between He and graphite.…”

Section: Introduction a Helium On Two-dimensional Materials: A Many-b...mentioning

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Two-Dimensional Bose-Hubbard Model for Helium on Graphene

Yu,

Lauricella,

Elsayed

et al. 2021

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An exciting development in the field of correlated systems is the possibility of realizing twodimensional (2D) phases of quantum matter. For a systems of bosons, an example of strong correlations manifesting themselves in a 2D environment is provided by helium adsorbed on graphene. We construct the effective Bose-Hubbard model for this system which involves hard-core bosons (U ≈ ∞), repulsive nearest-neighbor (V > 0) and small attractive (V < 0) next-nearest neighbor interactions. The mapping onto the Bose-Hubbard model is accomplished by a variety of many-body techniques which take into account the strong He-He correlations on the scale of the graphene lattice spacing. Unlike the case of dilute ultracold atoms where interactions are effectively point-like, the detailed microscopic form of the short range electrostatic and long range dispersion interactions in the helium-graphene system are crucial for the emergent Bose-Hubbard description. The result places the ground state of the first layer of 4 He adsorbed on graphene deep in the commensurate solid phase with 1/3 of the sites on the dual triangular lattice occupied. Because the parameters of the effective Bose-Hubbard model are very sensitive to the exact lattice structure, this opens up an avenue to tune quantum phase transitions in this solid-state system.

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Structure and superfluidity of He4 films on plated graphite

Cited by 10 publications

References 1 publication

Superfluidity of Atomically LayeredH4eFilms

Superfluidity of Atomically LayeredH4eFilms

Atomically Layered Helium Films at Ultralow Temperatures: Model Systems for Realizing Quantum Materials

Two-Dimensional Bose-Hubbard Model for Helium on Graphene

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