Superfluid Response of Parahydrogen Clusters in Superfluid $$^4$$ 4 He
- PDF / 800,488 Bytes
- 7 Pages / 439.37 x 666.142 pts Page_size
- 98 Downloads / 206 Views
Superfluid Response of Parahydrogen Clusters in Superfluid 4He Massimo Boninsegni1 Received: 20 June 2020 / Accepted: 25 June 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract First-principle computer simulations yield evidence of a finite superfluid response at low temperature of a parahydrogen cluster of 15 molecules in bulk superfluid 4 He. The superfluid fraction is worth ∼ 44 % at T = 0.25 K, growing to about ∼ 66% at T = 0.15 K, i.e., it is substantially reduced compared to that of the same cluster in vacuo, due to higher molecular localization. The implications of these findings on the interpretation of experiments with linear molecules embedded in parahydrogen clusters immersed in superfluid helium are discussed. Keywords Superfluidity · Quantum clusters · Quantum Monte Carlo
1 Introduction Almost half a century since the original prediction of Ginzburg and Sobyanin [1] of a possible superfluid transition at low temperature of a fluid of parahydrogen (p-H2 ) molecules, its observation has eluded even the ablest experimenters and/or cleverest approaches. Meanwhile, there is now a wealth of robust theoretical predictions, based on the state-of-the-art many-body techniques and realistic intermolecular potentials, pointing to the following: (a) Molecular hydrogen has a strong tendency to crystallize at temperatures well above those at which Bose condensation and superfluidity (SF) should occur, even in reduced dimensions [2, 3], disorder [4–6] and confinement [7, 8] (b) Even if a metastable fluid phase of p-H2 could be stabilized well below its 13.8 K freezing temperature,1 it may only turn superfluid at temperatures at least two 1
There are neither theoretical predictions nor experimental evidence suggesting that a p-H 2 crystal might display superfluid behavior. See, for instance [9]. * Massimo Boninsegni [email protected] 1
Department of Physics, University of Alberta, Edmonton, Alberta T6G 2E1, Canada
13
Vol.:(0123456789)
Journal of Low Temperature Physics
orders of magnitude lower than that (few K) predicted in the original 1973 work [10]. To date, the only quantitative prediction of superfluid behavior of p-H2 has been made not for the bulk phase, but for small clusters (few tens of molecules), at temperatures of the order of 1 K [11–14]. Experimentally, the superfluid behavior of a quantum cluster can be inferred from the free rotation of a linear molecule embedded in it, as shown by high-resolution microwave or infrared spectroscopy [15]. This methodology has allowed for the remarkable observation of superfluidity in 4 He clusters of just a few atoms [16] and has also yielded some evidence of possible superfluid behavior of p-H2 clusters comprising around fifteen molecules [17–19], in some cases backed by theoretical results [18, 20]. In some of these experiments [17, 21–24], the p-H2 clusters are immersed in relatively large superfluid 4 He nanodroplets (comprising several hundreds to several thousands of atoms), rendering this a potentially uniq
Data Loading...
