Electronic band structure, Fermi surface, and elastic properties of polymorphs of the 5.2 K iron-free superconductorSrPt2As2from first-principles calculations

Abstract

By means of first-principles calculations, we studied in detail the structural, elastic, and electronic properties of the tetragonal CaBe 2 Ge 2 -type 5.2 K superconductor SrPt 2 As 2 in comparison with two hypothetical SrPt 2 As 2 polymorphs with ThCr 2 Si 2 -type structures, which differ in the atomic configurations of the [Pt 2 As 2 ] (or [As 2 Pt 2 ]) blocks. We found that CaBe 2 Ge 2 -type SrPt 2 As 2 is a unique system with near-Fermi bands of a complicated character and an "intermediate"-type Fermi surface, which consists of electronic pockets having a cylinderlike [two-dimensional (2D)] topology (typical of 122 FeAs phases) together with 3D-like electronic and hole pockets, which are characteristic of ThCr 2 Si 2 -like iron-free low-T c superconductors. Our analysis revealed that, as distinct from ThCr 2 Si 2 -like 122 phases, other features of CaBe 2 Ge 2 -like SrPt 2 As 2 are as follows: (1) There are essential differences in the contributions from [Pt 2 As 2 ] and [As 2 Pt 2 ] blocks to the near-Fermi region; conduction is anisotropic and occurs mainly in the [Pt 2 As 2 ] blocks. (2) A 3D system of strong covalent Pt-As bonds is formed (inside and between [Pt 2 As 2 ] and [As 2 Pt 2 ] blocks), which is responsible for enhanced stability of this polymorph.(3) There is essential charge anisotropy between adjacent [Pt 2 As 2 ] and [As 2 Pt 2 ] blocks. We also predict that CaBe 2 Ge 2 -like SrPt 2 As 2 is a mechanically stable and relatively soft material with high compressibility, which will behave in a ductile manner. In contrast, the ThCr 2 Si 2 -type SrPt 2 As 2 polymorphs, which contain only [Pt 2 As 2 ] or [As 2 Pt 2 ] blocks, are less stable, have Fermi surfaces of a multisheet three-dimensional type like the ThCr 2 Si 2 -like iron-free 122 phases, and therefore will be ductile materials with high elastic anisotropy. Based on our data for the three simplest SrPt 2 As 2 polymorphs we assume that there may exist a family of higher-order polytypes, which can be formed as a result of various stackings of the two main types of building blocks ([Pt 2 As 2 ] and [As 2 Pt 2 ]) in various combinations along the z axis. This may provide an interesting platform for further theoretical and experimental search for other superconducting materials.

Evidence for two energy gaps and Fermi liquid behavior in the SrPt2As2superconductor

“…In contrast to other 122 Fe-based superconductors, this ironfree SrPt 2 As 2 adopts a different CaBe 2 Ge 2 -type structure. Its structure can be viewed as consisting of Pt 2 As 2 tetrahedral layers alternating with As 2 Pt 2 layers stacked along the c-axis, the former layers with the Pt ion located in the center of each As tetrahedron and the lat- * Electronic address: xiaofeng.xu@hznu.edu.cn † Electronic address: ghcao@zju.edu.cn ter layer the opposite [8]. Remarkably, in analogy to Febased pnictides, the SrPt 2 As 2 compound also shows a structural phase transition at ∼470K, which is associated with charge-density-wave (CDW) formation [7].…”

Two-Band Calculations on the Superconducting Property of SrPt $$_{2}\mathrm{As}_{2}$$ 2 As 2

“…Research shows that SrPt 2 As 2 does not preserve the ThCr 2 Si 2 -type structure, but adopts a tetragonal CaBe 2 Ge 2 -type structure [21][22][23]. Moreover, SrPt 2 As 2 has a higher critical temperature T c ∼ 5 K [23][24][25][26] than other iron-free AM 2 As 2 . For its special nature, SrPt 2 As 2 attracts much attention.…”

“…X-ray and early structural analyses show that the lattice parameters are a = 4.5279 Å and c = 10.0137 Å [22]. The Fermi surface of SrPt 2 As 2 consists of three electronic sheets and one hole-like sheet [23]. Under certain circumstances, the case of multiple Fermi surface sheets can lead to the existence of multiple superconducting energy gaps in one system, such as MgB 2 .…”

“…To further understand the nature of these systems, a series of iron-free 122 phases AM 2 As 2 (M is a nonmagnetic or magnetic 5d or 3d metal of group VIII, such as Ni, Co, Ru, Pd, Ir, or Rh) have been studied both experimentally and theoretically [10][11][12][13][14][15][16][17][18][19][20]. Research shows that SrPt 2 As 2 does not preserve the ThCr 2 Si 2 -type structure, but adopts a tetragonal CaBe 2 Ge 2 -type structure [21][22][23]. Moreover, SrPt 2 As 2 has a higher critical temperature T c ∼ 5 K [23][24][25][26] than other iron-free AM 2 As 2 .…”

Phase transition, elastic and thermodynamical properties of TcC under high pressure from first-principles calculations

“…The bulk modulus B and the shear modulus G can be defined from the elastic constants C ij according to the VoigtReuss-Hill average scheme [29]. The bulk modulus B V and shear modulus G V of WC TcC can be obtained by the VoigtReuss approximation as in the following equations [30]:…”