|
Geometric frustration arises when lattice structure prevents simultaneous minimization of local interaction energies. It leads to highly degenerate ground states and, subsequently, to complex phases of matter, such as water ice, spin ice, and frustrated magnetic materials. Closely packed colloidal spheres confined between parallel walls self-assemble into a buckled triangular lattice with either up or down displacements, reminiscent of the frustrated antiferromagnetic Ising model on a triangular lattice. We use microgel spheres with a temperature-sensitive diameter to tune the packing density which in turn sets the strength of the effective antiferromagnetic interaction between neighboring spheres. The micrometer length-scale of the spheres enables direct visualization of the 'spin' dynamics at the single-particle level. Our joint experimental and theoretical work reveals glassy dynamics which are governed by in-plane lattice distortions that partially relieve frustration and produce ground states with zigzagging stripes and subextensive entropy. The results we obtain for the structure and dynamics of this soft-matter system shed light on the nature of excitations and on the role of elasticity in geometrically-frustrated systems.
References: [1] Y. Han, Y. Shokef, A.M. Alsayed, P. Yunker, T.C. Lubensky, and A.G. Yodh, Nature 456, 898 (2008) [2] Y. Shokef and T.C. Lubensky, Phys. Rev. Lett. 102, 048303 (2009) |
|