Paramagnetism and reentrant behavior in quasi-1D superconductors at high magnetic fields

The thermodynamics of quasi-one-dimensional superconductors in the presence of large magnetic fields is studied. When the quantum effects of the magnetic field are taken into account, several reentrant phases persist at very high fields. In the last reentrant phase, the free energy, the specific heat jump and the excess magnetization are estimated near the critical temperature. In particular, the excess magnetization is found to be paramagnetic as opposed to diamagnetic (in weak fields) and its sign is found to be controlled by the slope of Hc2. This result is further generalized to the entire phase diagram (including all quantum phases) and to different physical systems using general thermodynamic relations which show that the sign of the excess magnetization ΔM near Hc2(T) follows dHc2(T)/dT. These relations provide a scenario for the evolution of the sign of ΔM from weak fields to strong fields