Observation of a remarkable reduction of correlation effects in BaCr2As2 by ARPES

TL;DR

This study uses ARPES and calculations to show that BaCr2As2 exhibits reduced electron correlation effects compared to similar materials, supporting the significance of Hund's exchange interaction in these systems.

Contribution

It provides experimental and theoretical evidence that correlation effects decrease in BaCr2As2, highlighting the role of Hund's exchange interaction in this class of materials.

Findings

Reduced correlation-induced mass renormalization in BaCr2As2

Lower lifetime broadening indicating weaker correlations

Supports Hund's exchange as a key factor in correlation strength

Abstract

The superconducting phase in iron based high Tc superconductors (FeSC) as in other unconventional superconductors such as the cuprates neighbours a magnetically ordered one in the phase diagram. This proximity hints at the importance of electron correlation effects in these materials, and Hund exchange interaction has been suggested to be the dominant correlation effect in FeSCs because of their multiband nature. By this reasoning, correlation should be strongest for materials closest to a half filled 3d shell (Mn compounds, hole doped FeSCs) and decrease for systems with both higher (electron doped FeSCs) and lower (Cr pnictides) 3d counts. Here we address the strength of correlation effects in BaCr2As2 by means of angle resolved photoelectron spectroscopy (ARPES) and first principles calculations. This combination provides us with two handles on the strength of correlation, First, a comparison of the experimental and calculated effective masses yields the correlation induced mass renormalisation. In addition, the lifetime broadening of the experimentally observed dispersions provides another measure of the correlation strength. Both approaches reveal a reduction of electron correlation in BaCr2As2 with respect to systems with a 3d count closer to five. Our results thereby support the theoretical predictions that Hund's exchange interaction is important in these materials.