Thermodynamic property of the Δ-chain

A one-dimensional fully frustrated quantum spin system called the Δ-chain is investigated, particularly with respect to the low-temperature structure of the specific heat, by quantum Monte Carlo simulations using the restructuring method. Sizes of the systems we considered are N=32, 48 and 64. The simulation results together with the diagonalization results for N=10 and 16 show that the size dependence of the data is very weak, and thus the second peak of the specific heat stably exists at T<0.1, which corresponds to less than half the spin gap. Locality of excitations is seen in the Monte Carlo snapshot. We consider that the low-temperature properties of this system are governed by the local elementary excitations which generate the Schottky-type specific heat peak in the background of the ordinary thermal specific heat.