First-principles study of the electronic structure of heavy fermion YbRh2Si2

The electronic properties of YbRh2Si2 are studied by means of band structure calculations based on the density functional theory within the LDA ( local density approximation), LDA+U, and fully relativistic scheme. The 4f derived bands are studied within a relativistic framework which yields flat and spin orbit split bands, and a correlated band method (LDA+U) that includes correlation corrections. In both cases the uppermost 4f band is located roughly 150 meV below the Fermi energy E-F, and hybridizes weakly with the dispersive Rh 4d bands and a Rh 4d(xy) band that does not disperse perpendicular to the Rh layers. When we applied the fully relativistic scheme, the 4f derived bands split into j = 7/2 and 5/2 excitations due to spin-orbit coupling effects. The f(7/2) multiplet is located much closer to E-F, hybridizing anisotropically with a Rh 4d derived conduction band. This mixing induces a non-integer occupation of the f levels n(f) and hence reveals that YbRh2Si2 is a mixed-valence heavy fermion. The 4f electrons can be delocalized through the hybridization with conduction electrons. And the hybridization between f and conduction d electrons plays a important role in YbRh2Si2. The Fermi surface splits into three different non-touching sheets. There are two tiny cylinder Fermi surfaces around Z points which are from the Rh 4d bands and the larger Fermi surfaces are from the 4f derived bands.