Thermodynamics of the planar Hubbard model

The thermodynamic properties of specific heat, entropy, chemical potential, spin susceptibility χₛ, and charge susceptibility χc are studied as functions of temperature and doping within the two-dimensional Hubbard model with various $U/t=4--12.$ Quantities are calculated using the finite-temperature Lanczos method with additional phase averaging for a system of 4×4 sites. Results show that the entropy at low T reaches a maximum near half-filling at the electron density n~1±0.15 in the whole regime of studied $U/t.$ The pseudogap in χₛ(T) becomes clearly pronounced for $U/t>~8$ while χc shows a maximum close to half-filling. The relation of results to those within the t-J model and to experiments is discussed.