From Fermi Arcs to Nodal Metal: Scaling of the Pseudogap with Temperature and Doping

The pseudogap phase in the cuprates is a most unusual state of matter$^{1-4}$: it is a metal, but its Fermi surface is broken up into disconnected segments known as Fermi arcs$^{5}$. Using angle resolved photoemission spectroscopy, we show that the anisotropy of the pseudogap in momentum space and the resulting arcs depend only on the ratio \textit{T/T*(x)}, where \textit{T*(x)} is the temperature below which the pseudogap first develops at a given hole doping, \textit{x}. In particular, the arcs, which extend at \textit{T*} to the hot spots where the antiferromagnetic zone boundary crosses the Fermi surface, collapse linearly with \textit{T/T*} and extrapolate to zero extent as \textit{T} 0. This suggests that the \textit{T} = 0 state is a nodal liquid, a strange metallic state whose gapless excitations are located only at points in momentum space, just as for a \textit{d-wave} superconductor.