The spectral weight of hole doped cuprates across the pseudogap critical point

TL;DR

This study investigates the evolution of spectral weight in hole-doped cuprates across the pseudogap critical point using infrared spectroscopy, revealing insights into carrier density, mass enhancement, and the superconducting dome.

Contribution

It provides detailed measurements of spectral weight changes across p* and links these to carrier density and coupling effects, offering a deeper understanding of the pseudogap transition.

Findings

Spectral weight K* is less than a third of band calculation predictions.

KMIR forms a doping-dependent dome, indicating coupling effects.

Smooth doping dependence of K* aligns with carrier density and mass enhancement data.

Abstract

One of the most widely discussed features of the cuprate high Tc superconductors is the presence of a pseudogap in the normal state. Recent transport and specific heat measurements have revealed an abrupt transition at the pseudogap critical point, denoted p*, characterized by a drop in carrier density and a strong mass enhancement. In order to give more details about this transition at p*, we performed low-temperature infrared spectroscopy in the normal state of cuprate superconductors La2-xSrxCuO4 (LSCO) and La1.8-xEu0.2SrxCuO4 (Eu-LSCO) for doping contents across the pseudogap critical point p* (from p = 0.12 to 0.24). Through the complex optical conductivity we can extract the spectral weight, K*, of the narrow Drude peak due the coherent motion of the quasi-particles, and the spectral weight enclosed inside the mid-infrared (MIR) band, KMIR, caused by coupling of the quasi-particles to collective excitations of the many-body system. K* is smaller than a third of the value predicted by band calculations, and KMIR forms a dome as a function of doping. We observe a smooth doping dependence of K* through p*, and demonstrate that this is consistent with the observed doping dependence of the carrier density and the mass enhancement. We argue that the superconducting dome is the result of the confluence of two opposite trends, namely the increase of the density of the quasi-particles and the decrease of their coupling to the collective excitations as a function of doping.