Metastable filamentary superconductivity with Tc = 10.2 K was observed in SrPt2Ge2. This is the highest Tc reported outside the iron-based 122-layer compounds. The stable phase for this compound is a non-superconducting monoclinic LaPt2Ge2-type structure with lattice parameters a = 0.4401(4) nm, b = 0.4435(4) nm, c = 0.9764(10) nm, β = 90.5°-90°. Weak diamagnetic shielding signal indicates that superconductivity is not from the major monoclinic phase, but from the minor BaFe2As2-type body-center-tetragonal (122-bct) phase with a = 0.44 nm, c = 0.98 nm, β = 90 °. Investigation on the pseudoternary system Sr(Pd1-xPtx) 2Ge2 suggests that the stable bct to monoclinic structure phase transition occurs near x = 0.15. For x < 0.15 with bct phase, bulk Tc increases from 3.2 K for SrPd2Ge2 to 3.6 K for SrPd 1.8 Pt 0.2 Ge2. For x > 0.15 with metastable filamentary bct phase, Tc increases from 7.5 K for x = 0.5 to 9.2 K for x = 0.7 and reaches a Tc maximum of 10.2 K for SrPt2Ge 2. High Tc is due to a strong quasi-2D Pt-Ge-Pt 5d xz,yz-4p-5dxz,yz hybridization in the Pt-Ge layer with squeezed-along-c-axis PtGe4 tetrahedral crystal field and Pt-5d 8 spin-orbital interaction in the metastable filamentary bct phase and is another example of multi-band (dxz/dyz/d xy) non-conventional s-wave superconductor.
ASJC Scopus subject areas
- Physics and Astronomy(all)