  It has long been a challenge to describe the origin of unconventional
superconductivity. The two known examples with high Tc, based on iron and
copper, have very different electronic structures, while other materials with
similar electronic structure may not show superconductivity at all. In this
paper, the authors show that by using high accuracy diffusion Monte Carlo
calculations, the unconventional superconductors of both high Tc types form a
cluster at intermediate spin-charge coupling. The spin-charge coupling may
serve as a normal state marker for unconventional superconductivity, and
provides evidence that unconventional superconductivity is due to interaction
of charge with local spins in materials.
