Electronic structures of ferromagnetic superconductors $\mathrm{UGe}_2$ and $\mathrm{UCoGe}$ studied by angle-resolved photoelectron spectroscopy

TL;DR

This study investigates the electronic structures of ferromagnetic superconductors UGe2 and UCoGe using angle-resolved photoelectron spectroscopy, revealing itinerant U 5f electrons and significant hybridization effects near the Fermi level.

Contribution

It provides experimental insights into the electronic structures of UGe2 and UCoGe, highlighting deviations from band-structure calculations and the role of hybridization in their properties.

Findings

U 5f electrons exhibit itinerant character near the Fermi level.

Band structures largely explained by calculations treating U 5f electrons as itinerant.

Strong hybridization between U 5f and Co 3d states in UCoGe.

Abstract

The electronic structures of the ferromagnetic superconductors $\mathrm{UGe}_2$ and $\mathrm{UCoGe}$ in the paramagnetic phase were studied by angle-resolved photoelectron spectroscopy using soft X-rays ($h\nu =400-500$). The quasi-particle bands with large contributions from $\mathrm{U}~5f$ states were observed in the vicinity of $E_\mathrm{F}$, suggesting that the $\mathrm{U}~5f$ electrons of these compounds have an itinerant character. Their overall band structures were explained by the band-structure calculations treating all the $\mathrm{U}~5f$ electrons as being itinerant. Meanwhile, the states in the vicinity of $E_\mathrm{F}$ show considerable deviations from the results of band-structure calculations, suggesting that the shapes of Fermi surface of these compounds are qualitatively different from the calculations, possibly caused by electron correlation effect in the complicated band structures of the low-symmetry crystals. Strong hybridization between $\mathrm{U}~5f$ and $\mathrm{Co}~3d$ states in $\mathrm{UCoGe}$ were found by the $\mathrm{Co}~2p-3d$ resonant photoemission experiment, suggesting that $\mathrm{Co}~3d$ states have finite contributions to the magnetic, transport, and superconducting properties.