Search for Cooper-pair Fluctuations in Severely Underdoped YBCO Films

Y. L. Zuev, I. Hetel, T. R. Lemberger

The preformed-pairs theory of pseudogap physics in high-$T_C$ superconductors predicts a nonanalytic $T$-dependence for the $ab$-plane superfluid fraction, ${\rho }_S$, at low temperatur…