Thermodynamic evidence for electron correlation-driven flattening of the quasiparticle bands in the high-Tc cuprates

TL;DR

Thermodynamic measurements in high-Tc cuprates reveal significant electron correlation-driven band flattening, emphasizing the role of Van Hove singularities and impacting theories on effective mass divergence and superconducting pairing mechanisms.

Contribution

This study provides thermodynamic evidence for stronger electron correlation effects and band flattening in cuprates than previously indicated, challenging existing interpretations of calorimetry data.

Findings

Enhanced band flattening due to electron correlations.

Van Hove singularity influences calorimetry measurements.

Band flattening constrains maximum Tc via phase fluctuations.

Abstract

A flattened electronic band is one of several possible routes for increasing the strength of the pairing interactions in a superconductor. With this in mind, we show here that thermodynamic measurements of the high-Tc cuprates reveal an appreciably stronger electron correlation-driven flattening of the quasiparticle bands than has previously been indicated. Specifically, we find that thermodynamic measurements indicate an electronic entropy in excess of that that can be accounted for by the value of the universal Fermi velocity inferred from photoemission experiments. The observed band flattening implies that the Van Hove singularity features prominently in calorimetry measurements, causing it undermine prior arguments for a divergence in the renormalization of the effective mass near a critical doping $p^\ast$ based on calorimetry measurements. The band flattening is also sufficient to drive the cuprates into a strong pairing regime where the maximum transition temperature becomes constrained by phase fluctuations.