Modeling of the electronic state of the High-Temperature Superconductor LaCuO: Phonon dynamics and charge response

TL;DR

This paper models the electronic and phonon behavior of LaCuO across different doping levels, linking charge response, phonon dynamics, and superconducting phases, and compares predictions with experimental data.

Contribution

It introduces a comprehensive modeling approach connecting orbital transitions, phonon modes, and charge response in LaCuO, elucidating the normal and superconducting states.

Findings

Supports the modeling with phonon calculations and experimental data.

Predicts phonon dispersion in the overdoped regime.

Suggests a crossover between phase ordering and quasiparticle pairing near optimal T_C.

Abstract

A modeling of the normal state of the p-doped high-temperature superconductors (HTSC's) is presented. This is achieved starting from a more conventional metallic phase for optimal- and overdoping and passing via the underdoped to the insulating state by consecutive orbital selective compressibility-incompressibility transitions in terms of sum rules for the charge response. The modeling is substantiated by corresponding phonon calculations. Extending investigations of the full dispersion and in particular of the strongly doping dependent anomalous phonon modes in LaCuO, which so far underpin our treatment of the density response of the electrons in the p-doped HTSC's, gives additional support for the modeling of the electronic state, compares well with recent experimental data and predicts the dispersion for the overdoped regime. Moreover, phonon densities of states have been calculated and compared for the insulating, underdoped, optimally doped and overdoped state of LaCuO. From our modeling of the normal state a consistent picture of the superconducting phase also can be extracted qualitatively pointing in the underdoped regime to a phase ordering transition. On the other hand, the modeling of the optimal and overdoped state is consistent with a quasi-particle picture with a well defined Fermi surface. Thus, in the latter case a Fermi surface instability with an evolution of pairs of well defined quasiparticles is possible and can lead to a BCS-type ordering. So, it is tempting to speculate that optimal $T_C$ in the HTSC's marks a crossover region between these two forms of ordering.