Experimental investigation of electronic interactions in collapsed and uncollapsed LaFe2As2 phases

TL;DR

This study compares the electronic interactions in collapsed and uncollapsed LaFe2As2 phases, revealing higher electron correlations in the superconducting uncollapsed phase despite similar electron-phonon coupling.

Contribution

It provides experimental evidence of differing electron correlations in LaFe2As2 phases, highlighting their potential role in superconductivity.

Findings

Higher electron correlations in uncollapsed phase

Similar electron-phonon coupling in both phases

Structural transition correlates with superconductivity

Abstract

The iron-based pnictide LaFe2As2 is not superconducting as-synthesized, but it becomes such below Tc around 12 K upon annealing, as a consequence of a structural transition from a phase with collapsed tetragonal crystal structure to an uncollapsed phase. In this work, we carry out specific heat, Raman spectroscopy and normal state electric and thermoelectric transport measurements in the collapsed and uncollapsed LaFe2As2 phases to gain insight into the electron interactions and their possible role in the superconducting pairing mechanism. Despite clear features of strong electron-phonon coupling observed in both phases, neither the low energy phonon spectra nor the electron-phonon coupling show significant differences between the two phases. Conversely, the Sommerfield constants are significantly different in the two phases, pointing to much higher electron correlation in the superconducting uncollapsed phase and confirming theoretical studies.