Spin-1/2 Heisenberg antiferromagnet on the kagome´ lattice: High-temperature expansion and exact-diagonalization studies

For the spin-1/2 Heisenberg antiferromagnet on the kagomé lattice we calculate the high-temperature series for the specific heat and the structure factor. A comparison of the series with exact-diagonalization studies shows that the specific heat has further structure at lower temperature in addition to a high-temperature peak at T≊2/3. At T=0.25 the structure factor agrees quite well with results for the ground state of a finite cluster with 36 sites. At this temperature the structure factor is less than two times its T=∞ value and depends only weakly on the wave vector q, indicating the absence of magnetic order and a correlation length of less than one lattice spacing. The uniform susceptibility has a maximum at T≊1/6 and vanishes exponentially for lower temperatures.