TUNNELING STUDY ON Ba2Ca3Cu4O8(O1-xFx)2
Abstract
We report the tunneling conductance on a quadruple-layered cuprate, Ba2Ca3Cu4O8(O1-xFx)2 (2x~1.4, Tc~100K) that includes inequivalent outer (OP) and inner (IP) CuO2 planes in a unit cell. Typical tunneling conductance displays the spectral dip structures as well as the superconducting gap (SCG) with clear coherence peaks. However we sometimes observe a pseudogap (PG) like structure without coherence peak at 4.2K. The magnitude of PG at 4.2K is larger than that of SCG at 4.2K and its conductance curve displays a faint structure at low energy. Therefore its origin would be different from that of small-PG observed at above Tc. In addition, we find that there are two kinds of SCGs that originate from IP and OP, and this result suggests that the superconducting property at IP is different from that at OP because of the imbalance of doped carrier between IP and OP. The observation of large PG at low temperature suggests the existence of some form of hidden ordered state at T<Tc and it would coexist with superconductivity.
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