Preliminary Heat Capacity and Vapor Pressure Measurements of 2D 4He on ZYX Graphite

Nakamura, Sachiko; Matsui, Koji; Matsui, Tamao; Fukuyama, Hiroshi

doi:10.1007/s10909-012-0847-5

Cited by 10 publications

(12 citation statements)

References 11 publications

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“…Specifically, the 3-state Potts model predicts that near the transition, the heat capacity C(T ) is proportional to |T − T c| −α , where T c is the critical temperature and α=1/3. The agreement with the measured critical value (α = 0.34 ± 0.01) for this transition on graphite represents a major success for both theory and experiment [40,41,44].…”

Section: Monolayer Quantum Films On Graphitesupporting

confidence: 73%

“…This full monolayer phase is an incommensurate 2D solid for both helium and hydrogen. We note that the very high density reflects a factor [40]; there also appears one curve for 4 He/Grafoil, from Greywall [25]; see also Ecke et al [41]. On this surface (area 30.5 m 2 ), a classical ideal gas would have C = 2.68 mJ/K of 3 compression relative to the 2D ground state phase density (ρ ∼ 0.04 atoms/ Å2 ).…”

Section: Monolayer Quantum Films On Graphitementioning

confidence: 68%

“…One significant example is the commensurate solid melting transition, for which the specific heat C(N, T ) of 4 He is shown in Fig. 6 for two varieties of graphite substrate [40,24,41]. The dramatic peaks in the data rise a factor 10 above the value expected for a 2D classical ideal gas: C/(Nk B ) = 1, i.e.…”

Section: Monolayer Quantum Films On Graphitementioning

confidence: 95%

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Novel behaviors of monolayer quantum gases on Graphene, Graphane and Fluorographene

Reatto,

Galli,

Nava

et al. 2013

Preprint

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This article discusses the behavior of submonolayer quantum films (He and H 2 ) on graphene and newly discovered surfaces that are derived from graphene. Among these substrates are graphane (abbreviated GH), which has an H atom bonded to each C atom, and fluorographene (GF). The subject is introduced by describing the related problem of monolayer films on graphite. For that case, extensive experimental and theoretical investigations have revealed that the phase diagrams of the bose gases 4 He and para-H 2 are qualitatively similar, differing primarily in a higher characteristic temperature scale for H 2 than for He. The phase behaviors of these films on one side of pristine graphene, or both sides of free-standing graphene, are expected to be similar to those on graphite. We point out the possibility of novel phenomena in adsorption on graphene related to the large flexibility of the graphene sheet, to the non-negligible interaction between atoms adsorbed on opposite sides of the sheet and to the perturbation effect of the adsorbed layer on the Dirac electrons. In contrast, the behaviors predicted on GF and GH surfaces are very different from those on graphite, a result of the different corrugation, i.e., the lateral variation of the potential experienced by these gases. This arises because on GF, for example, half of the F atoms are located above the C plane while the other half are below this plane. Hence, the He and H 2 gases experience a very different potentials from those on graphite or graphene. As a result of this novel geometry and potential, distinct properties are observed. For example, the 4 He film's ground-state on graphite is a two-dimensional (2D) crystal commensurate with the substrate, the famous √ 3 × √ 3 R30 o phase; on GF and GH, instead, it is predicted to be an anisotropic superfluid. On GF the anisotropy is so extreme that the roton excitations are very anisotropic, as if the bosons are moving in a multiconnected space along the bonds of a honeycomb lattice. Such a novel phase has not been predicted or observed previously on any substrate. Also, in the case of 3 He the film's ground-state is a fluid, thus offering the possibility of studying an anisotropic Fermi fluid with a tunable density. The exotic properties expected for these films are discussed along with proposed experimental tests.

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Section: Monolayer Quantum Films On Graphitesupporting

confidence: 73%

Section: Monolayer Quantum Films On Graphitementioning

confidence: 68%

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Novel behaviors of monolayer quantum gases on Graphene, Graphane and Fluorographene

Reatto,

Galli,

Nava

et al. 2013

Preprint

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“…1 of Ref. 23) and for that of 3 He as well [24]. The commensurability of the C1 phase is with respect to the graphite honeycomb lattice.…”

mentioning

confidence: 99%

Possible quantum liquid crystal phases of helium monolayers

Nakamura

Matsui

et al. 2016

Phys. Rev. B

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The second-layer phase diagrams of 4 He and 3 He adsorbed on graphite are investigated. Intrinsically rounded specific-heat anomalies are observed at 1.4 and 0.9 K, respectively, over extended density regions in between the liquid and incommensurate solid phases. They are identified to anomalies associated with the Kosterlitz-Thouless-Halperin-Nelson-Young type two-dimensional melting. The prospected low temperature phase (C2 phase) is a commensurate phase or a quantum hexatic phase with quasi-bond-orientational order, both containing zero-point defectons. In either case, this would be the first atomic realization of the quantum liquid crystal, a new state of matter. From the large enhancement of the melting temperature over 3 He, we propose to assign the observed anomaly of 4 He -C2 phase at 1.4 K to the hypothetical supersolid or superhexatic transition. PACS numbers: 67.80.bd, 67.80.dm, 67.80.de Quantum liquid crystal (QLC) is a novel state of matter in nature. It is a quantum phase with partially broken rotational and/or translational symmetries and fluidity (or superfluidity) even at T = 0. The electronic nematic phase, which is conceptually one of the QLCs, is recently being studied in a variety of materials [1, 2]. Atomic or molecular QLCs are more intuitive and direct quantum counterparts of classical liquid crystal. In bosonic systems, superfluid QLC or supersolidity is also expected. Recently the latter possibility has intensively been explored in bulk solid 4 He [3][4][5], and the former is proposed in cold dipolar molecule gases in two dimensions (2D) [6]. The predicted stripe phase of superfluid 3 He in slab geometry is a candidate for fermionic QLC [7, 8]. However, all previous experimental attempts to detect atomic or molecular QLCs have not yet been successful or still are under debate.Atomic monolayer of helium (He) adsorbed on a strongly attractive graphite surface provides a unique arena to investigate novel quantum phenomena of bosons ( 4 He: spinless) and fermions ( 3 He: nuclear spin 1/2) in 2D. Particularly the prospected commensurate phase in the second layer of He (hereafter the C2 phase) is a hopeful candidate for atomic QLC because of a delicate balance among the kinetic (∼10 K), He-He interaction (∼10 K) and corrugated potential energies (≤ 3 K). The commensurability here is with respect to the triangular lattice of the compressed first He layer. The fermionic QLC might be a new perspective for the gapless quantum spin-liquid nature [9] and the anomalous thermodynamic behavior below 100 mK of the 3 He -C2 phase [10] alternative to the multiple spin exchange model [11] or others [12].If the 4 He -C2 phase is a QLC, the supersolid ground state can be expected. Eventually, two previous torsional oscillator experiments on this system observed a reentrant superfluid response as a function of density below 0.4 K [13, 14]. However, the identification of the phenomenon is left controversial, since the detected superfluid fractions are limited to 0.01-0.02, and the density regions where th...

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“…A striking feature was the formation of a √ 3 × √ 3 commensurate solid, registered with the substrate, in which 1/3 of the graphite basal plane hexagons are occupied. This was identified from a sharp melting peak near 3K; the width of this anomaly is reduced when using a substrate of larger platelet size (ZYX exfoliated graphite) [8,9].…”

Section: Some Historymentioning

confidence: 99%

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

2020

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Preliminary Heat Capacity and Vapor Pressure Measurements of 2D 4He on ZYX Graphite

Cited by 10 publications

References 11 publications

Novel behaviors of monolayer quantum gases on Graphene, Graphane and Fluorographene

Novel behaviors of monolayer quantum gases on Graphene, Graphane and Fluorographene

Possible quantum liquid crystal phases of helium monolayers

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

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