Finite-temperature crossover phenomenon in the S=1/2 antiferromagnetic Heisenberg model on the kagome lattice

Thermal properties of the $S=1/2$ kagome Heisenberg antiferromagnet at low temperatures are investigated by means of the Hams-de Raedt method for clusters of up to 36 sites possessing a full symmetry of the lattice. The specific heat exhibits, in addition to the double peaks, the third and the forth peaks at lower temperatures. With decreasing the temperature, the type of the magnetic short-range order (SRO) changes around the third-peak temperature from the $\sqrt{3} \times \sqrt{3}$ to the $q$=0 states, suggesting that the third peak of the specific heat is associated with a crossover phenomenon between the spin-liquid states with distinct magnetic SRO. Experimental implications are discussed.