$T_c$ Dependence of Energy Gap and Asymmetry of Coherence Peaks in NdBa${}_2$Cu${}_3$O${}_{7-\delta }$

Abstract

We report here the results of scanning tunneling spectroscopic experiments performed on hole doped NdBa${}_2$Cu${}_3$O${}_{7-\delta }$ single crystals of $T_c$ values of 76 K, 93.5 K and 95.5 K. The energy gaps are observed to be increasing with decreasing $T_c$ values. The coherence peaks are asymmetric with the peaks at the filled states being larger than those at the empty ones. The asymmetry increases with decreasing $T_c$. The observed asymmetry and its $T_c$ dependence can be explained by considering the Mott insulating nature of the material at the undoped state.

4 pages, 1 Figure, to appear in Euro Phys. Lett

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