Localized Bose-Einstein condensation in disordered liquidHe4films

Abstract

We present neutron scattering measurements of the phonon-roton and layer modes of liquid helium films adsorbed in 25Å pore diameter gelsil as a function of temperature. The goal is to determine whether the well-defined phonon-roton and layer modes observed at low temperature at partial fillings of the porous media persist as well-defined modes at higher temperatures above the superfluid phase, as is the case of fully filled pores (3D liquid). We find that well defined P-R modes exist in films at temperatures well above the superfluid phase. This is the case at all fillings investigated. Liquid 4 He in porous media is an example of a Bose liquid in disorder. The existence of P-R modes above Tc suggests the existence of patches or islands of Bose condensed liquid having long range order (localized Bose-Einstein condensation (LBEC)) above Tc. The interpretation is that the welldefined P-R modes propagate in the patches of BEC. Gelsil partially filled with liquid helium shows the same LBEC behavior as found previously in fully filled gelsil (as in a 3D liquid).

Excitations in the quantum liquid4He: A review

“…Above T λ there is only broad, largely temperature independent intensity. Data on liquid 4 He under pressure in porous media (Bossy et al 2015), where the P-R mode vanishes at lower temperature (less broadening), suggest that the intensity in the mode can vanish at T T λ with little broadening.…”

“…We do not cover 4 He films, (2D or 1D systems) nor helium in porous media (reduced dimensions and quant um liquids in disorder). For recent articles see Bertaina et al (2016), Gordillo and Boronat (2016), Vranješ Markić and Glyde (2015), Godfrin et al (2012), Diallo et al (2014), Bossy et al (2012aBossy et al ( , 2015 and Prisk et al (2013). We do not consider helium droplets nor the cold Bose gases.…”