SHEAR MELTING OF CONFINED SOLID MONOLAYER FILMS

Strain-induced melting of solid phases in a prototypal slit pore [a monatomic fluid constrained between two plane-parallel walls made up like atoms fixed in the configuration of the (100) plane of the face-centered cubic lattice] is investigated by Monte Carlo calculations in the ''isostress-isostrain'' ensemble where the thermodynamic state of the pore phase is uniquely determined by a fixed number of molecules, constant load or normal stress and constant temperature. If the walls are properly aligned laterally, a commensurate solid phase can form epitaxially. Moving the walls out of alignment (shear strain) creates a distorted solid, which reacts (shear stress) by tending to realign the walls. If the shear strain is increased beyond a critical value, the solid begins to melt. However, melting is a continuous transition which does not immediately lead to a normal liquid, but rather a disordered phase that sustains a non-negligible shear stress. Shear melting is contrasted to ordinary melting at constant normal stress, which appears to be a first-order transition.