Phase diagram of a mesoscopic superconducting Pb square: Ballistic Hall magnetometry

Ballistic Hall magnetometry is used to investigate the magnetization of a mesoscopic superconducting Pb square as a function of magnetic field (H) and temperature (T). Vortex penetration and expulsion fields are determined from magnetization curves at different temperatures below T(c) and are combined in an experimental T-H phase diagram. Enhanced stability of the symmetry-matching vorticities L=1 and L=4 is observed. The experimental results are compared with theoretical calculations using the nonlinear Ginzburg-Landau theory for a thin square.