Colossal band renormalization and stoner ferromagnetism induced by electron-antiferromagnetic-magnon coupling

TL;DR

This study reveals how electron-antiferromagnetic magnon interactions cause significant band renormalization and induce ferromagnetism in Ba$_{1-x}$K$_x$Mn$_2$As$_2$, with implications for understanding correlated materials.

Contribution

It provides the first direct observation of strong electron-antiferromagnetic magnon interactions and their doping and temperature dependence, revealing their role in ferromagnetism.

Findings

EAIs induce a kink in band dispersion

Coupling constant of EAIs can reach up to 6

EAIs exhibit strong doping and temperature dependence

Abstract

The interactions between electrons and antiferromagnetic magnons (AFMMs) are important for a large class of correlated materials. For example, they are the most plausible pairing glues in high-temperature superconductors, such as cuprates and iron pnictides. However, unlike electron-phonon interactions (EPIs), clear-cut observations regarding how electron-AFMM interactions (EAIs) affect the band structure are still lacking. Consequently, critical information on the EAIs, such as its strength and doping dependence, remains elusive. Here we directly observe that EAIs induces a kink structure in the band dispersion in Ba$_{1-x}$K$_x$Mn$_2$As$_2$, and subsequently unveil several key characteristics of EAIs. We found that the coupling constant of EAIs can be as large as 6, and it shows huge doping dependence and temperature dependence, all in stark contrast to the behaviors of EPI and beyond our current understanding of EAIs. Such a colossal renormalization of electronic bands by EAIs drives the system to the Stoner criteria, giving the intriguing ferromagnetic state in Ba$_{1-x}$K$_x$Mn$_2$As$_2$. Our results expand the current knowledge of EAIs, which may facilitate the further understanding of many correlated materials where EAIs play a critical role, such as high-temperature superconductors.