Confinement-induced columnar crystals of ellipses

Densest-packed structures of identical ellipses within a parallel strip have been obtained through Monte Carlo simulations and analytic derivations. Each of such structures is an affine transformation of a particular densest-packed structure of identical circular disks. Three types of structures have been identified: Types X and Y correspond, respectively, to affine stretches along the perpendicular and axial directions of the parallel strip, and type M corresponds to affine stretches of locally densest structures. Our findings enrich the field of condensed matter physics with a class of confinement-induced, orientationally ordered crystal structures, and offer possibilities of developing low-dimensional materials with specific orientational ordering.