Doping dependence of the pseudogap in Pr$_{2-x}$Ce$_x$CuO$_4$

The temperature dependence of the in-plane tunneling conductance was measured for many doping levels of Pr$_{2-x}$Ce$_{x}$CuO$_{4}$ (PCCO) x=0.11-x=0.19 using planar lead/Insulator/PCCO junctions on thin films and single crystals. At low temperatures and zero field the lead features are clearly seen, indicating good tunnel junctions with negligible leakage currents. When superconductivity in the PCCO electrode is quenched a normal state gap is seen at all doping levels studied. We find it to vanish above a certain temperature T*. T* is greater than T$_{c}$ for the underdoped region and it follows T$_{c}$ on the overdoped side. This behavior suggests finite pairing amplitude above T$_{c}$ on the underdoped side. The data and interpretation differ from previously publish ones [1]. [1] L. Alff \textit{et al. }Nature (London) 422, 698 (2003).