Anomalous Normal State Transport in Underdoped Cuprates: A Preformed-Pair Alternative to the Vortex Scenario
We address those puzzling experiments in underdoped high $T_c$ superconductors which have been associated with normal state "vortices" and show these data can be understood as deriving from preformed pairs with onset temperature $T^* > T_c$. For uncorrelated bosons in small magnetic fields, and arbitrary $T^*/T_c$, we present the exact contribution to \textit{all} transport coefficients. In the overdoped regime our results reduce to those of fluctuation theories ($T^*\approx T_c$). Semi-quantitative agreement with Nernst, ac conductivity and diamagnetic measurements is quite reasonable.