NMR evidence for common superconducting and pseudogap phase diagrams of Y Ba 2 Cu 3 O 7 − δ and La 2 − x Sr x Ca Cu 2 O 6

We report ac susceptibility and $^{17}\mathrm{O}$ nuclear-magnetic-resonance (NMR) measurements on the double-Cu${\mathrm{O}}_{2}$-layer ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{6}$ high-temperature superconducting cuprate (HTSC) with a ${T}_{c,max}$ of 60 K. A comparison is made with $^{89}\mathrm{Y}$ NMR measurements on $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$, which has a higher ${T}_{c,max}$ of 93 K and ${\mathrm{Y}}_{0.8}{\mathrm{Ca}}_{0.2}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ with a slightly lower ${T}_{c,max}$ of 87 K. We find that the hole concentration dependence of the normal-state gap and of ${T}_{c}$ both scale with ${T}_{c,max}$, implying a universal scaled phase diagram for these two superconductors, and, by implication, for the wider class of HTSC. This suggests that the normal-state gap and the pairing mechanism may have a common origin.