4 He glass phase: A model for liquid elements

International audienceThe specific heat of liquid helium confined under pressure in nanoporous material and the formation, in these conditions, of a glass phase accompanied by latent heat are known. These properties are in good agreement with a recent model predicting, in liquid elements, the formation of ultrastable glass having universal thermodynamic properties. The third law of thermodynamics involves that the specific heat decreases at low temperatures and consequently the effective transition temperature of the glass increases up to the temperature where the frozen enthalpy becomes equal to the predicted value. The glass residual entropy is about 23.6% of the melting entropy. Introduction The solid-liquid transformation of bulk helium depends on the pressure p and temperature T [1-6]. The melting entropy is determined from the Clapeyron relation knowing the volume and melting temperature changes associated with the solid-to-liquid transformation under a pressure p [2]. The phase diagram is deeply modified when liquid helium is confined in 25Ǻ mean diameter nano-pore media under pressures p where 3.58 ≤ p≤ 5.27 MPa [7]. Early studies of these involved specific heat anomaly measurements and they were viewed as a consequence of the formation of localized Bose-Einstein condensates on nanometer length scales analogous to a solid [7]. The glass phase has since been discovered using measurements of the static structure factor, S(Q), of helium confined in the porous medium MCM-41 with pore diameter 47±1.5 Å. A similar amorphous S(Q) was also observed in 34 Å Gelsil [8]. The presence of an amorphous phase has been confirmed at higher pressures using porous Vycor glass [9]. In this work we consider that the supercooled liquid far below the melting temperature T m is condensed in a glass phase accompanied by an exothermic latent heat associated with a first-order transition