High-temperature magnetic susceptibility in metal-electron systems

High-temperature magnetic susceptibility is studied using the Hubbard model. The equation in the high-temperature limit is derived from the Kubo formula as the Curie law of Ns free 1/2-spins, where Ns is the average number of electrons not forming singlets. Exact results for Ns are presented for various cases and are shown to depend only on the total number of electrons Ne and available orbital states, which is the number of lattices L in the single-band case. The condition of kBT≫U, W with the onsite repulsion U and bandwidth W gives Ns=Lp(2−p)/2 with filling p=Ne/L. The numerical calculation for U=0 shows that the universal Curie law holds at temperatures above the threshold temperature T0, compatible with the Fermi temperature. The threshold temperature for U>0 is found to be lower than T0. The application of the present results to a heavy-fermion system near the Mott transition is proposed.