First-Order Type Effects in YBa$_2$Cu$_3$O$_{6+x}$ at the Onset of Superconductivity

TL;DR

This study uses Raman scattering to investigate how charge ordering and lattice dynamics in YBa2Cu3O6+x change at the onset of superconductivity, revealing a link between charge order and superconducting transition.

Contribution

It provides new insights into the first-order effects of charge ordering on lattice and electronic properties at the critical doping level in YBa2Cu3O6+x.

Findings

Discontinuous changes in lattice and electron dynamics at p_sc1

Evidence of a diagonal superstructure below p_sc1

Charge ordering influences the maximum superconducting temperature

Abstract

We present results of Raman scattering experiments on tetragonal ${\rm (Y_{1-y}Ca_{y})Ba_{2}Cu_{3}O_{6+x}}$ for doping levels $p(x,y)$ between 0 and 0.07 holes/CuO$_2$. Below the onset of superconductivity at $p_{\rm sc1} \approx 0.06$, we find evidence of a diagonal superstructure. At $p_{\rm sc1}$, lattice and electron dynamics change discontinuously with the charge and spin properties being renormalized at all energy scales. The results indicate that charge ordering is intimately related to the transition at $p_{\rm sc1}$ and that the maximal transition temperature to superconductivity at optimal doping $T_{c}^{\rm max}$ depends on the type of ordering at $p>p_{\rm sc1}$.