High-resolution measurements of excitations in superfluid<sup>4</sup>He beyond the roton

Pearce, J. V.; Azuah, R. T.; Fåk, B.; Sakhel, Asaad R.; Glyde, H. R.; Stirling, W. G.

doi:10.1088/0953-8984/13/20/304

Cited by 24 publications

(30 citation statements)

References 16 publications

(50 reference statements)

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“…This latter broad feature is also seen in the superfluid (figure 1c), starting at a similar absolute momentum transfer (≈2.4 A −1 ) and a slightly lower energy, corresponding to approximately twice the minimum energy gap in each case. This feature is also seen in the normal fluid [19]. In the solid, the high energy excitation displays hexagonal symmetry about the origin.…”

Section: Resultsmentioning

confidence: 59%

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Neutron scattering study of the excitation spectrum of solid helium at ultra-low temperatures

et al. 2008

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There has been a resurgence of interest in the properties of solid helium due to the recent discovery of non-classical rotational inertia (NCRI) in solid 4 He by Chan and coworkers below 200 mK which they have interpreted as a transition to a 'supersolid' phase. We have carried out a series of elastic and inelastic neutron scattering measurements on single crystals of hcp 4 He at temperatures down to 60 mK. While we have found no direct evidence of any change in the excitation spectrum at low temperatures, we have found that the excitation spectrum of solid 4 He shows several interesting features, including extra branches in addition to the phonon branches. We interpret these extra branches as single particle excitations due to propagating vacancy waves, which map on to the famous 'roton minimum' long known in the excitation spectrum of superfluid liquid 4 He. The results show that in fact solid 4 He shares several features in common with the superfluid.

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Section: Resultsmentioning

confidence: 59%

“…In ref. [19], this scattering was identified as broad, multiphonon scattering. Alternatively, it might also be associated with strongly interacting single-particle scattering, in which case it should connect with the free particle recoil scattering at larger momentum transfers.…”

Section: Resultsmentioning

confidence: 99%

Neutron scattering study of the excitation spectrum of solid helium at ultra-low temperatures

et al. 2008

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“…We compare our results with experiments obtained at nonzero pressure and temperature from Ref. 32. The experiment presents a well-distinct peak along with a slowly decaying tail (generally interpreted as due to single-particle excitations 32,33 ).…”

Section: Application To Liquid Heliummentioning

confidence: 53%

“…32. The experiment presents a well-distinct peak along with a slowly decaying tail (generally interpreted as due to single-particle excitations 32,33 ). The theoretical curve shows instead a single peak in a position that is not very far from the overall centroid of the experimental response.…”

Section: Application To Liquid Heliummentioning

confidence: 93%

Dynamical structure functions from quantum Monte Carlo calculations of a proper integral transform

Roggero¹,

Pederiva²,

Orlandini³

2013

Phys. Rev. B

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An ab initio method for determining the dynamical structure function of an interacting many-body quantum system has been devised by combining a generalized integral transform method with quantum Monte Carlo (QMC) methods. A kernel has been found that (i) lets the transform be calculable with QMC methods and (ii) is a representation of the δ function, allowing an inversion of the transform with a much higher predictive power than the inverse Laplace transform. As a first application, the excitation spectrum of bulk atomic 4 He has been computed, both in the low and intermediate momentum ranges. The peculiar form of the kernel allows us to predict, without using any model, both positions and widths of the collective excitations in the maxon-roton region, as well as the existence of the second collective peak. A prediction of the dispersion of the single-particle modes described by the incoherent part is also presented.

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“…However, the connection between superfluidity and BEC via the condensate wave function survives. For example, superfluidity, BEC, and well defined P-R excitations still all appear at the same condensation temperature [13][14][15][16][17] T . In three dimensions superfluidity in a uniform fluid appears to be inseparably linked to the existence of BEC, a connection made in Tisza's two-fluid model of helium II.…”

Section: Introductionmentioning

confidence: 99%

Superfluidity and Bose-Einstein condensation in optical lattices and porous media: A path integral Monte Carlo study

Shams

Glyde

2009

Phys. Rev. B

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We evaluate the Bose-Einstein condensate density and the superfluid fraction of bosons in a periodic external potential using path-integral Monte Carlo methods. The periodic lattice consists of a cubic cell containing a potential well that is replicated along one dimension using periodic boundary conditions. The aim is to describe bosons in a one-dimensional optical lattice or helium confined in a periodic porous medium. The one-body density matrix is evaluated and diagonalized numerically to obtain the single boson natural orbitals and the occupation of these orbitals. The condensate fraction is obtained as the fraction of bosons in the orbital that has the highest occupation. The superfluid density is obtained from the winding number. From the condensate orbital and superfluid fraction, we investigate ͑1͒ the impact of the periodic external potential on the spatial distribution of the condensate, and ͑2͒ the correlation of localizing the condensate into separated parts and the loss of superflow along the lattice. For high-density systems, as the well depth increases, the condensate becomes depleted in the wells and confined to the plateaus between successive wells, as in pores between necks in a porous medium. For low-density systems, as the well depth increases the BEC is localized at the center of the wells ͑tight binding͒ and depleted between the wells. In both cases, the localization of the condensate suppresses superflow leading to a superfluid-insulator crossover. The impact of the external potential on the temperature dependence of the superfluidity is also investigated. The external potential suppresses the superfluid fraction at all temperatures, with a superfluid fraction significantly less than one at low temperature. The addition of an external potential does not, however, significantly reduce the transition temperature.

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High-resolution measurements of excitations in superfluid⁴He beyond the roton

Cited by 24 publications

References 16 publications

Neutron scattering study of the excitation spectrum of solid helium at ultra-low temperatures

Neutron scattering study of the excitation spectrum of solid helium at ultra-low temperatures

Dynamical structure functions from quantum Monte Carlo calculations of a proper integral transform

Superfluidity and Bose-Einstein condensation in optical lattices and porous media: A path integral Monte Carlo study

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High-resolution measurements of excitations in superfluid4He beyond the roton

Cited by 24 publications

References 16 publications

Neutron scattering study of the excitation spectrum of solid helium at ultra-low temperatures

Neutron scattering study of the excitation spectrum of solid helium at ultra-low temperatures

Dynamical structure functions from quantum Monte Carlo calculations of a proper integral transform

Superfluidity and Bose-Einstein condensation in optical lattices and porous media: A path integral Monte Carlo study

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High-resolution measurements of excitations in superfluid⁴He beyond the roton