Forming a cube from a sphere with tetratic order.

Composed of square particles, the tetratic phase is characterized by a fourfold symmetry with quasi-long-range orientational order but no translational order. We construct the elastic free energy for tetratics and find a closed form solution for ±1/4 disclinations in planar geometry. Applying the same covariant formalism to a sphere, we show analytically that within the one elastic constant approximation eight +1/4 disclinations favor positions defining the vertices of a cube. The interplay between defect-defect interactions and bending energy results in a flattening of the sphere towards superspheroids with the symmetry of a cube.