First-principle study on electronic and structural properties of newly discovered superconductors: CaIrSi3 and CaPtSi3

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Abstract

Electronic and structural properties of newly discovered superconductors CaIrSi3 and CaPtSi3 were investigated using ab initio band structure methods. The crystallographic data for CaPtSi3 were computed on the basis of a structural optimization method. The calculated electronic structure revealed similarities to that of the other noncentrosymmetric superconductor BaPtSi3.

Highlights

► Electronic structure of noncentrosymmetric superconductors CaIrSi3 and CaPtSi3 have been calculated. ► Full crystallographic data for CaPtSi3 have been found on the basis of a structural optimization method. ► The split of bands by the spin-orbit coupling is small which suggest BCS-like behavior. ► The Fermi surface of CaPtSi3 is similar to previously discovered BaPtSi3.

Introduction

The noncentrosymmetric superconductors have attracted attention due to their unique superconducting properties caused by the Rashba-type antisymmetric spin–orbit coupling which leads to a mixing of the spin-singlet and spin-triplet states [1]. Since the first heavy fermion noncentrosymmetric superconductor CePt3Si was discovered [2], a lot of similar systems have been found (e.g., UIr; see the review [3] and references therein). The noncentrosymmetric AMX3 compounds (A = Ca, Ba alkaline- or Ce rare-earth metals, M = transition metal, X = Si, Ge) represent a separate class of these materials. The majority of these systems are the cerium compounds [3] which are antiferromagnetic and become superconducting only under pressure. However, a few non-cerium compounds were reported recently: BaPtSi3 [4], CaIrSi3 [5], [6] and CaPtSi3 [6] which are superconducting at ambient pressure. The superconducting transition temperatures Tc for the latter compounds take the values of 2.25 K, 3.7 K and 2.3 K, respectively. In the current paper, electronic and structural properties of CaIrSi3 and CaPtSi3 are calculated within the density functional framework (cf. [7] and references therein).

Section snippets

Method of calculations

The density functional calculations were done with the use of three different ab inito codes: elk-1.0.0 (FP-LAPW method) [8], Quantum-Espresso package (pseudopotentials, QE package) [9], [10] and FPLO-9 [7], [11], [12]. The first one was used to calculate the electronic structure with and without the spin–orbit interaction (SOI). It was treated in a perturbative approach within GGA with PBE exchange-correlation functional [13]. The second code was applied to evaluate the structural parameters

Results and discussion

The results of the structure optimization are summarized in Table 1. As expected, the crystallographic data for CaIrSi3 obtained in different approximations are under- (LDA) and over-estimated (GGA), but the mean values are in reasonable agreement with experiment. The differences between the mean values of the LDA and GGA data and the experimental lattice constants in the case of CaIrSi3 amount to 0.003 Å and −0.029 Å for a and c lattice parameters, respectively. The corresponding differences in

Conclusion

To conclude, we have presented the calculations within the density functional approach of the electronic and structural properties of two newly discovered noncentrosymmetric superconductors CaIrSi3 and CaPtSi3. For the first compound, the calculations were made with the use of the experimental crystallographic data, for the second one the crystallographic data were computed on the basis of the structural optimization method relying on the data for the first compound. In the latter case, the

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