First-principles study of the electronic structure of heavy fermionYbRh2Si2

Abstract

The electronic properties of YbRh2Si2 are studied by means of band structure calculations based on thedensity functional theory within the LDA (local density approximation),LDA+U, and fully relativistic scheme. The 4f derived bands are studied within a relativisticframework which yields flat and spin–orbit split bands, and a correlated band method(LDA+U) that includes correlation corrections. In both cases the uppermost4f band is located roughly 150 meV below the Fermi energyEF, and hybridizes weakly with the dispersive Rh 4d bands and a Rh4dxy band that does not disperse perpendicular to the Rh layers. When weapplied the fully relativistic scheme, the 4f derived bands split intoj = 7/2 and 5/2 excitations due to spin–orbit coupling effects. Thef7/2 multiplet is locatedmuch closer to EF, hybridizing anisotropically with a Rh 4d derived conductionband. This mixing induces a non-integer occupation of the f levelsnf and hencereveals that YbRh2Si2 is a mixed-valence heavy fermion. The 4f electrons can be delocalized through the hybridization withconduction electrons. And the hybridization between f and conduction d electrons plays a importantrole in YbRh2Si2. The Fermi surface splits into three different non-touching sheets. There are two tinycylinder Fermi surfaces around Z points which are from the Rh 4d bands and the largerFermi surfaces are from the 4f derived bands.