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$_{6+\delta}$ (Pb-Bi-2201) across the end points of the pseudogap and superconducting phases was conducted using optical ultrafast time-resolved pump-probe spectroscopy. In the Pb-Bi-2201 near the proposed pseudogap end-point doping, the transient reflectivity dynamics above $T_{{\rm c}}$ resemble the pseudogap response observed in the optimally doped La-Bi-2201. With decreasing temperature, however, the relaxation time exhibits a power-law divergence, $\tau\sim10\hbar/k_{\mathrm{B}}T$, consistent with quantum critical behavior near the proposed pseudogap end-point doping. A similar power-law increase in relaxation time is also observed at a slightly more overdoped composition, though it is less pronounced.