Anomalous structural and mechanical properties of solids confined in quasi-one-dimensional strips.

We show using computer simulations and mean field theory that a system of particles in two dimensions, when laterally confined by a pair of parallel hard walls within a quasi-one-dimensional channel, possesses several anomalous structural and mechanical properties not observed in the bulk. Depending on the density rho and the distance between the walls Ly, the system shows structural characteristics analogous to a weakly modulated liquid, a strongly modulated smectic, a triangular solid, or a buckled phase. At fixed rho, a change in Ly leads to many re-entrant discontinuous transitions involving changes in the number of layers parallel to the confining walls depending crucially on the commensurability of interlayer spacing with Ly. The solid shows resistance to elongation but not to shear. When strained beyond the elastic limit, it fails undergoing plastic deformation but surprisingly, as the strain is reversed, the material completely recovers and returns to its original undeformed state. We obtain the phase diagram from mean field theory and finite size simulations and discuss the effect of fluctuations.