Hard X-ray angle-resolved photoemission spectroscopy reveals significant alterations in the valence band states of EuPd2Si2 at a temperature TV, where the Eu ions undergo a temperature-induced valence crossover from a magnetic Eu2+ state to a low-temperature valence-fluctuating state. The introduction of small amounts of Au on Pd lattice sites and Ge on Si sites, respectively, results in a decrease in TV and the emergence of an antiferromagnetic state at low temperatures without valence fluctuations. It has been proposed that the boundary between AFM order and valence crossover represents a first-order phase transition associated with a specific type of second-order critical end point. In this scenario, strong coupling effects between fluctuating charge, spin, and lattice degrees of freedom are to be expected. In the case of EuPd2(Si1−xGex)2 with x=0.13, which is situated close to the critical end point, a splitting of conduction band states and the emergence of flat bands with one-dimensional character have been observed. A comparison with ab initio theory demonstrates a high degree of correlation with experimental findings, particularly in regard to the bands situated in proximity to the critical end point.
@article{arxiv.2410.18597,
title = {The electronic structure of EuPd$_2$Si$_2$ in the vicinity of the critical endpoint},
author = {O. Fedchenko and Y. -J. Song and O. Tkach and Y. Lytvynenko and S. V. Chernov and A. Gloskovskii and C. Schlueter and M. Peters and K. Kliemt and C. Krellner and R. Valenti and G. Schoenhense and H. J. Elmers},
journal= {arXiv preprint arXiv:2410.18597},
year = {2024}
}