Critical photoinduced reflectivity relaxation dynamics in single-layer Bi-based cuprates near the pseudogap end point

Abstract

A comprehensive study of photoinduced transient reflectivity dynamics in heavily overdoped single-layer cuprate (Bi,Pb)${}_2$Sr${}_2$CuO${}_{6+\hat{I}´}$ (Pb-Bi2201), across the end points of the pseudogap and superconducting phases, has been conducted using optical ultrafast time-resolved pump-probe spectroscopy. In the Pb-Bi2201 just before reaching the pseudogap end point, the transient reflectivity dynamics above $T_{\mathrm{c}}$ resemble the pseudogap response observed in optimally doped La-Bi2201. At low temperatures, however, the relaxation time exhibits a power-law divergence, $\ddot{I}„\sim 10\hslash /k_{\mathrm{B}}T$, signaling quantum critical behavior at the pseudogap end point doping. A similar power-law increase in relaxation time is also observed in Pb-Bi2201 just beyond the pseudogap doping end point, though it is less pronounced.