Comparative study of electronic structure of new superconductors (Sr,Ca)Pd$_2$As$_2$ and related compound BaPd$_2$As$_2$

This paper presents the comparative study of LDA calculated electronic structure of new isostructural to iron based systems superconductors (Sr,Ca)Pd$_2$As$_2$ with T$_c$ about $1$ K and similar but structurally different system BaPd$_2$As$_2$. Despite chemical formula looks similar to iron superconductors and even main structural motif is the same – layers of Fe square lattices, electronic structure of (Sr,Ca)Pd$_2$As$_2$ and BaPd$_2$As$_2$ differs from Fe(As,Se)-HTSC completely. All these systems have essentially three dimensional Fermi surfaces in contrast to Fe(As,Se) materials. The Fermi level is crossed by low intensive tails of Pd-$4d$ and As-$4p$ states. However (Sr,Ca)Pd$_2$As$_2$ and BaPd$_2$As$_2$ materials have rather well developed peaks of Pd-$4d$($x^2-y^2$) band. Thus by doping of about 2 holes per unit cell one can increase density of states at the Fermi level by a factor about 2.5. Since experimentally these compounds were found to be simple BCS superconductors the hole doping may considerably increase T$_c$. LDA calculated total densities of states at the Fermi level for stoichiometric systems perfectly agree with experimental estimates signifying rather small role of electronic correlations.