Universal scaling laws can guide the understanding of new phenomena, and forcuprate high-temperature superconductivity such an early influential relationshowed that the critical temperature of superconductivity ($T_c$) correlateswith the density of the superfluid measured at low temperatures. This famousUemura relation has been inspiring the community ever since. Here we show thatthe charge content of the bonding orbitals of copper and oxygen in theubiquitous CuO$_2$ plane, accessible with nuclear magnetic resonance (NMR), istied to the Uemura scaling. This charge distribution between copper and oxygenvaries between cuprate families and with doping, and it allows us to draw a newphase diagram that has different families sorted with respect to their maximum$T_c$. Moreover, it also shows that $T_c$ could be raised substantially if wewere able to synthesize materials in which more oxygen charge is transferred tothe approximately half filled copper orbital.
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