BOOKS: The Quest for Absolute Zero

Mendelssohn, K.; Bhagat, S. M.

doi:10.1119/1.2351182

Cited by 10 publications

(14 citation statements)

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“…The corresponding kinetic energies are ͗K͘ϭ14.45Ϯ0.3, ͗K͘ϭ14.7Ϯ0.3, and ͗K͘ϭ16.3Ϯ0.3 K at Tϭ0.5, 1.6, and 2.3 K, respectively. ͑17͒, ␤ 5 ϭā 52 /(Q) 3 . That is, ␤ 5 Q 3 is largely independent of Q.…”

Section: Resultsmentioning

confidence: 99%

“…Superfluidity in liquid 4 He has a long and rich history of study [1][2][3][4][5][6][7][8] and BEC has recently been demonstrated spectacularly in dilute Bose gases. [9][10][11][12][13] Einstein 14 first showed that a gas of particles obeying the statistics proposed by Bose 15 could condense into a state having macroscopic occupation of a single-particle quantum state ͑BEC͒ below a critical temperature T c .…”

Section: Introductionmentioning

confidence: 99%

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Condensate, momentum distribution, and final-state effects in liquid4He

2000

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We present benchmark, high precision measurements of the dynamic structure factor J(Q,y) of liquid 4 He at several temperatures over a wide wave vector transfer range 15рQр29 Å Ϫ1 . J(Q,y) is very different in the superfluid phase below T and in the normal phase above T where T ϭ2.17 K. Below T , J(Q,y) contains a pronounced additional contribution near yϭ0 that is asymmetric about yϭ0, reflecting a condensate contribution modified by asymmetric final-state ͑FS͒ effects. The asymmetry in J(Q,y) is direct qualitative evidence of a condensate. We analyze the data at all T using the same model of J(Q,y) consisting of a condensate fraction n 0 , a momentum distribution n*(k) for states kϾ0 above the condensate, and a FS broadening function R(Q,y). We find a condensate fraction given by n 0 (T)ϭn 0 (0)͓1Ϫ(T/T ) ␥ ͔ with n 0 (0)ϭ(7.25Ϯ0.75)% and ␥ϭ5.5Ϯ1.0 for TϽT , which is 30% below existing observed values, and n 0 ϭ(0Ϯ0.3)% for TϾT . We determine n(k) in both phases. The n*(k) is significantly narrower than a Gaussian in both superfluid and normal 4 He and narrowest in the normal phase. The final-state function is determined from the data and is the same within precision above and below T . The precise form of R(Q,y) is important in determining the value of n 0 (T) below T . When independent, theoretical R(Q,y) are used in the analysis, the n 0 (T) is found to be the same as or smaller than the above value.where បk is the 4 He atom momentum in the fluid, n(k) is the momentum distribution, and ប R ϭប 2 Q 2 /2m and v R ϭបQ/m are the free 4 He atom recoil energy and velocity, respectively. S IA (Q,) depends solely on n(k).At finite Q, interactions of the recoiling atom with its neighbors, denoted final-state ͑FS͒ effects, contribute to S(Q,). The observed S(Q,) is then 21,6,7

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Condensate, momentum distribution, and final-state effects in liquid4He

2000

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“…Revealing the nature of liquid 4 Hein confined media and on surfaces has played a central role in understanding superfluidity. 1,2 The early demonstrations of superfluidity itself in the 1930s were made by showing the remarkable flow properties of liquid 4 He in powders, [3][4][5] which confine the helium to short length scales and create large surface areas.…”

Section: Introductionmentioning

confidence: 99%

Excitations of superfluid4Hein porous media: Aerogel and Vycor

et al. 2001

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We present precision neutron scattering measurements of the dynamic structure factor S(Q,) and the elementary excitations of liquid 4 He immersed in aerogel and Vycor. In both porous media, liquid 4 He supports two-dimensional ͑2D͒ layer modes at wave vectors in the roton region that propagate in the liquid layers adjacent to the media walls. The layer modes have a rotonlike energy dispersion relation with energies that are consistent with specific heat and superfluid density measurements at low temperature. Liquid 4 He in these media also supports 3D phonon-roton ͑p-r͒ excitations that have energies and lifetimes at temperatures 0.5рTр2.3 K which are the same as in bulk liquid 4 He within current precision (5 eV͒. The layer modes are the only new excitations observed in these disordering media to date. In Vycor, we observe a well-defined p-r excitation at temperatures above T c in the normal phase. This suggests that there is a localized condensate ͑phase coherence on short length scales͒ above T c in Vycor.

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“…Both these condensed phases are transparent insulators. Prior to their syntheses many scientists had predicted that the condensed phases would be metals at atmospheric pressure (Mendelssohn 1966). This prediction was based on the assumption that hydrogen would be a monatomic alkali metal, as the elements below hydrogen in the first column of the Periodic Table. Instead, hydrogen turned out to be a diatomic insulator, as the halogens in the seventh column of the Periodic Table. Later, Wigner and Huntington (1935) predicted theoretically that the insulating molecular solid would transform to a metallic monatomic solid at sufficiently high pressure P and density D at temperature T = 0 K. Over the years the predicted pressure of this transition has varied from 25 GPa (Wigner and Huntington 1935) to 2,000 GPa (Alder and Christian 1960).…”

Section: Introductionmentioning

confidence: 99%

Metallization of fluid hydrogen at 140 GPa (1.4Mbar) by shock compression

Nellis

2000

High Pressure Research

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Shock compression was used to produce the first observation of a metallic state of condensed hydrogen. The conditions of metallization are a pressure of 140 GPa (1.4 Mbar), 0.6 g/cm 3 (ninefold compression of initial liquid-H2 density), and 3000 K. The relatively modest temperature generated by a reverberating shock wave produced the metallic state in a warm fluid at a lower pressure than expected previously for the crystallographically ordered solid at low temperatures. The relatively large sample diameter of 25 mm permitted measurement of electrical conductivity. The experimental technique and data analysis are described.

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BOOKS: The Quest for Absolute Zero

Cited by 10 publications

References 0 publications

Condensate, momentum distribution, and final-state effects in liquid4He

Condensate, momentum distribution, and final-state effects in liquid4He

Excitations of superfluid4Hein porous media: Aerogel and Vycor

Metallization of fluid hydrogen at 140 GPa (1.4Mbar) by shock compression

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