THE HINGE BEHAVIOR OF THE CURRENT VOLTAGE CHARACTERISTICS OF POLYCRYSTALLINE HIGH-TEMPERATURE SUPERCONDUCTORS

Polycrystalline high temperature superconductors often exhibit a linear relationship between ln(V) and ln(I). We observe that measurements made at a variety of temperatures and magnetic fields commonly produce a family of linear behaviours which pass very close to a "hinge point" if extrapolated from the linear region to higher currents. We have investigated this behaviour by fitting data taken from two phases of BiSCCO to an empirical formula which contains temperature and magnetic field dependent parameters describing the intercept, slope and curvature of the ln(V) versus ln(I) behaviour. We show that the concept of the "hinge" is still valid even when the curvature is non-zero. Equivalent pairs of magnetic field and temperature give the same slope and intercept while spanning two clearly distinguishable high and low magnetic field regions of behaviour. This evidence indicates the need for a theory in which low field and high field behaviour are due to the same physical phenomena.