Pseudogap like tunneling spectra in electron doped high-temperature superconductors

Abstract

We have measured the low-energy quasiparticle excitation spectrum of the electron doped high-temperature superconductors (HTS) Nd 1.85Ce 0.15CuO 4− y and Pr 1.85Ce 0.15CuO 4− y as a function of temperature and applied magnetic field using grain-boundary junction tunneling spectroscopy. For these optimum doped samples, no excitation gap is observed in the tunneling spectra above the superconducting critical temperature. In contrast, in applied magnetic fields above the resistively determined upper critical field, a clear excitation gap at the Fermi level of comparable size to the superconducting energy gap is present. One possible interpretation of this observation is the existence of a normal state pseudogap also in the electron doped HTS.