Electronic structure and magnetism in UGa2: DFT+DMFT approach

TL;DR

This paper uses advanced computational methods (DFT+DMFT) to clarify the electronic structure and magnetism of UGa2, showing improved agreement with experimental magnetic moments and electronic properties.

Contribution

It demonstrates that L(S)DA+DMFT accurately captures the magnetic moments and electronic structure of UGa2, addressing limitations of traditional band theory.

Findings

L(S)DA+DMFT reproduces experimental magnetic moments.

Correlations shift 5f states away from the Fermi level.

Reduced Sommerfeld coefficient aligns with experimental specific heat data.

Abstract

The debate whether uranium 5f electrons are closer to being localized or itinerant in the ferromagnetic compound UGa2 is not yet fully settled. The experimentally determined magnetic moments are large, approximately 3 Bohr magnetons, suggesting the localized character of the 5f electrons. In the same time, one can identify signs of itinerant as well as localized behavior in various spectroscopic observations. The band theory, employing local exchange-correlation functionals, is biased toward itinerant 5f states and severely underestimates the moments. Using material-specific dynamical mean-field theory (DMFT), we probe how a less approximate description of electron-electron correlations improves the picture. We present two variants of the theory: starting either from spin-restricted (LDA) or spin-polarized (LSDA) band structure. We show that the L(S)DA+DMFT method can accurately describe the magnetic moments in UGa2 as long as the exchange interaction between the uranium 6d and 5f electrons is preserved by a judicious choice of the spin-polarized double-counting correction. We discuss the computed electronic structure in relation to photoemission experiments and show how the correlations reduce the Sommerfeld coefficient of the electronic specific heat by shifting the 5f states slightly away from the Fermi level.