Superfluidity of metastable glassy bulkpara-hydrogen at low temperature

Abstract

Molecular para-hydrogen (p-H 2 ) has been proposed theoretically as a possible candidate for superfluidity, but the eventual superfluid transition is hindered by its crystallization. In this work, we study a metastable noncrystalline phase of bulk p-H 2 by means of the path integral Monte Carlo method in order to investigate at which temperature this system can support superfluidity. By choosing accurately the initial configuration and using a noncommensurate simulation box, we have been able to frustrate the formation of the crystal in the simulated system and to calculate the temperature dependence of the one-body density matrix and of the superfluid fraction. We observe a transition to a superfluid phase at temperatures around 1 K. The limit of zero temperature is also studied using the diffusion Monte Carlo method. Results for the energy, condensate fraction, and structure of the metastable liquid phase at T = 0 are reported and compared with the ones obtained for the stable solid phase.

Possible superfluidity of molecular hydrogen in a two-dimensional crystal phase of sodium

“…1 Intermolecular H 2 -H 2 interactions are attractive and quite intense; hence, even though hydrogen molecules are lighter than 4 He atoms, p-H 2 crystallization is energetically favored over melting in the T → 0 limit frustrating any possibility to observe superfluidity (SF) or Bose-Einstein condensation (BEC) in bulk. Putting this into numbers, molecular hydrogen becomes a solid at temperatures below T t ∼ 14 K, whereas the critical temperature at which BEC and SF are expected to occur is T c ∼ 1 K. 2 In spite of that, many experimental attempts have focused on supercooling bulk liquid p-H 2 below T c , although unfortunately with no apparent success to date. 3,4 A likely way to induce superfluidity in molecular hydrogen consists in lowering its melting temperature by reducing its dimensionality and/or confining it to restricted geometries.…”

Observation of crystallization slowdown in supercooled parahydrogen and orthodeuterium quantum liquid mixtures

“…However, diverse drawbacks such as polydispersity and sedimentation often make the experimental data from these systems difficult to interpret [8,9]. Accessing the details of the crystallization process in simple atomic and molecular counterparts, on the other hand, remains an experimental challenge due to relevant time scales that are orders of magnitude shorter.Theoretical studies have shown that the inclusion of quantum effects adds a further degree of complexity in the behavior of supercooled liquids, leading to novel exotic phenomena such as superfluidity [10,11] or enhanced dynamical slowing down [12][13][14]. Yet again, the difficulties in supercooling a quantum liquid to very low temperatures have so far precluded possible experimental studies of the interplay of quantum effects and structural transformations in nonequilibrium bulk liquids.…”

“…Theoretical studies have shown that the inclusion of quantum effects adds a further degree of complexity in the behavior of supercooled liquids, leading to novel exotic phenomena such as superfluidity [10,11] or enhanced dynamical slowing down [12][13][14]. Yet again, the difficulties in supercooling a quantum liquid to very low temperatures have so far precluded possible experimental studies of the interplay of quantum effects and structural transformations in nonequilibrium bulk liquids.…”

“…We have simulated mixtures of up to 300 molecules in boxes with periodic boundary conditions with 0, 3, and 10% oD 2 at T = 13 K, with 50% oD 2 at T = 14.5 K, and with 90, 97, and 100% oD 2 at T = 17 K. In order to avoid the crystallization of the mixtures we followed the strategy reported in Ref. [11], verifying that the particles in the simulation cell remained in a disordered metastable configuration for a sufficiently large number (∼10 4 ) of Monte Carlo steps to ensure a reliable characterization of their physical properties. We have also verified that these latter were dependent only on the temperature and the density of the simulated system but not on the particular Monte Carlo stochastic trajectory sampled by checking that the results obtained from statistically independent simulations were consistent with each other.…”

Mixing effects in the crystallization of supercooled quantum binary liquids

“…We used a number of particles and a simulation box with sideratios non-compatible with close-packed crystal lattices; moreover, we generated the starting disordered configuration for our simulations as reported in Ref. 37. The validity of our choices has been checked by computing the probability distributions p(Q 4 ,Q 6 ) for the ordered and disordered configurations, shown in Fig.…”