The structure of liquid helium in nanoconfinement

Liquid 4He has long served as a model and relatively accessible system in which to study boson phase transitions in disordered quantum matter. In particular, the lambda-transition at 2.17 K leads to a superfluid Bose-Einstein condensate (BEC) which has been studied extensively by both experimental and theoretical methods. To this day, the nature of coherence in the liquid state arising from the formation of a BEC in liquid 4He remains a fundamental and challenging topic, with ramifications across condensed matter physics and quantum many-body systems, and beyond, even into cosmology and particle physics. The aim of this proposal is to measure the structure factor of liquid 4He in the bulk and in nanoscale confinement of MCM-41 (pore diameter 5 nm), in both the normal and superfluid states at 4.0 K and 2.0 K. By exploiting the extended Q-range and high count-rate of NIMROD we will be able to determine at high-resolution the local and intermediate-range structure of 4He. We will therefore be able to detect even subtle changes in liquid structure on formation of a BEC, but also to determine via MCM-41 pore-pore Bragg peak intensity any changes in pore-filling and/or small angle scattering. Thus, new insight into an archetypal strongly interacting quantum liquid.