SHAPE-DEFORMATION-DRIVEN STRUCTURAL TRANSITIONS IN QUANTUM HALL SKYRMIONS

The quantum Hall ground state away from v = 1 can be described by a co llection of interacting Skyrmions. We show within the context of a non linear sigma model that the classical ground state away from v = 1 is a Skyrmion crystal with a generalized Neel order. As a function of fil ling factor v and Lande factor g, the Skyrmion crystal undergoes a tri angle --> square --> triangle transition at zero temperature. We argue that this structural transition is driven by a change in the shape of the individual Skyrmions and may be probed experimentally. Quantum fl uctuations lead to an orientationally disordered phase at low Skyrmion densities.