The Distribution of the Energy Gap and Josephson IcRn Product in Bi2212 by Tunneling Spectroscopy

Abstract

We present direct measurements of the density of states by tunneling spectroscopy on slightly overdoped Bi2212 single crystals at low temperature using break-junction and point-contact techniques. We find that (i) the variation of the gap magnitude, Delta, between 20 and 36 meV is likely to be intrinsic to the Bi2212, and (ii) there is a correlation between the maximum value of the Josephson IcRn product and the gap magnitude: IcRn decreases with the increase of Delta. The maximum IcRn value of 26 mV is observed at Delta = 20.5 meV. For Delta = 36.5 meV, the maximum measured value of IcRn is 7.3 mV. We conclude that (i) the distribution of the Josephson IcRn product as a function of gap magnitude can not be explained by the presence of a single energy gap in Bi2212, and (ii) the coherence energy scale in Bi2212 has the maximum Josephson strength.