Effects of Fermi-surface shrinking on the optical sum rule in pnictides

TL;DR

This study examines how band shifts due to spin-fluctuation coupling affect the optical sum rule in pnictides, revealing spectral weight transfer and implications for experimental measurements.

Contribution

It demonstrates that Fermi-surface shrinking does not significantly change charge-carrier concentration but causes spectral weight transfer, impacting optical sum rule analysis.

Findings

Charge-carrier concentration remains nearly unchanged despite Fermi-surface shrinking.

Significant spectral weight transfer from coherent to incoherent processes occurs.

Experimental sum rule estimates are affected by finite cut-off integration.

Abstract

In this paper we investigate the effects of the band shifts induced by the interband spin-fluctuation coupling on the optical sum rule in pnictides. We show that, despite the shrinking of the Fermi surfaces with respect to first-principle calculations, the charge-carrier concentration in each band is almost unchanged, with a substantial conservation of the total optical sum rule. However, a significant transfer of spectral weight occurs from low-energy coherent processes to incoherent ones, with practical consequences on the experimental estimate of the sum rule, that is carried out integrating the data up to a finite cut-off. This has profound consequences both on the absolute value of the sum rule and on its temperature dependence, that must be taken into account while discussing optical experiments in these systems.