Mechanism for lifting the degeneracy in the double-exchange spin ice model on a kagome lattice: Dodecamer formation

We investigated the double-exchange spin ice model on a kagome lattice by Monte-Carlo simulation in order to study a mechanism for lifting the degeneracy in frustrated electron systems. We show specific heat and vector spin chirality data on a finite lattice. Specific heat has a double-peak structure: a broad and a sharp peak are at kBT/t∼0.15 and 0.015, respectively, where t is the transfer integral of electrons. The broad peak corresponds to a crossover to the spin ice-like state, on the other hand, the sharp one is a transition to a dodecagonal spin cluster (dodecamer) state. We discuss the interplay between the formation of the dodecamer state and the lifting of the macroscopic degeneracy