Specific heat and magnetization of superconducting niobium in the mixed state

The thermodynamics of the mixed state of niobium is reconsidered. Critical fieldsH_c(t),H_c1(t),and H_c2(t), Maki parameters ₁ and ₂, magnetization, and specific heat are measured with a computer-controlled magnetometer and calorimeter. The results show quantitative discrepancies with the isotropic Gorkov-Brandt theory over almost the whole mixed state. Computations based on Fermi surface anisotropy using a scaling ofH_c2 provide a much better agreement with the experimental magnetization curves already in the limit of weak nonlocality, thus suggesting a numerical evaluation of the anisotropic terms in the Gorkov-Brandt theory.