Role of electron-electron interactions in the charge dynamics of rare-earth-doped CaFe2As2

TL;DR

This study explores how electron-electron interactions influence charge transport in rare-earth-doped CaFe2As2, revealing saturation of scattering rates, spectral weight loss, and the impact of structural transitions on electronic correlations.

Contribution

It provides new insights into the role of electron-electron interactions and their temperature dependence in doped CaFe2As2, highlighting phenomena observed at energy scales much larger than the Fermi energy.

Findings

Scattering rate saturates at the Mott-Ioffe-Regel limit above 200 K.

Spectral weight is lost with increasing temperature and recovered at higher energy scales.

Electronic correlations weaken below the structural collapse transition at 70 K.

Abstract

We have investigated the charge dynamics and the nature of many-body interactions in La- and Pr- doped CaFe2As2. From the infrared part of the optical conductivity, we discover that the scattering rate of mobile carriers above 200 K exhibits saturation at the Mott-Ioffe-Regel limit of metallic transport. However, the dc resistivity continues to increase with temperature above 200 K due to the loss of Drude spectral weight. The loss of Drude spectral weight with increasing temperature is seen in a wide temperature range in the uncollapsed tetragonal phase, and this spectral weight is recovered at energy scales about one order of magnitude larger than the Fermi energy scale in these semimetals. The phenomena noted above have been observed previously in other correlated metals in which the dominant interactions are electronic in origin. Further evidence of significant electron-electron interactions is obtained from the presence of quadratic temperature and frequency-dependent terms in the scattering rate at low temperatures and frequencies in the uncollapsed tetragonal structures of La-doped and Pr-doped CaFe2As2. For temperatures below the structure collapse transition in Pr-doped CaFe2As2 at 70 K, the scattering rate decreases due to weakening of electronic correlations, and the Drude spectral weight decreases due to modification of the low-energy electronic structure.