NMR Evidence for ad-Wave Normal-State Pseudogap

Abstract

NMR data from high- $T_c$ superconducting cuprates having widely different $T_{c,\max }$ values and different hole concentrations, $p$, are shown to implicate a $d$-wave-like pseudogap. The deduced pseudogap energies agree well with the gap in the charge excitations determined from photoemission measurements, and the gap energies scale with $T_{c,\max }$. The pseudogap and superconducting gap thus have the same energy scale and for different cuprates have a universal $p$ dependence.