Orientational behavior of quantum rotors physisorbed on boron nitride

Abstract

We report the results of NMR studies of the two-dimensional (2D) phase diagrams for molecular ${\mathrm{H}}_{2}$ films (monolayers and submonolayers) adsorbed on BN for ortho-${\mathrm{H}}_{2}$ concentrations 0.30.745 and temperatures 0.054.2 K. A 2D quadrupolar glass state has been identified for submonolayer coverages for 0.480.69 and 0.2\ensuremath{\leqslant}T\ensuremath{\leqslant}0.6 K. For submonolayer films (75% of full monolayer), an orientationally ordered phase (expected pinwheel structure) was observed for X\ensuremath{\geqslant}0.69 with a transition to a second distinct ordered phase (expected herringbone structure) for X\ensuremath{\leqslant}0.69.