Interrogating the superconductor Ca10(Pt4As8)(Fe2−xPtxAs2)5 Layer-by-layer

Abstract

Ever since the discovery of high-Tc superconductivity in layered cuprates, the roles that individual layers play have been debated, due to difficulty in layer-by-layer characterization. While there is similar challenge in many Fe-based layered superconductors, the newly-discovered Ca10(Pt4As8)(Fe2As2)5 provides opportunities to explore superconductivity layer by layer, because it contains both superconducting building blocks (Fe2As2 layers) and intermediate Pt4As8 layers. Cleaving a single crystal under ultra-high vacuum results in multiple terminations: an ordered Pt4As8 layer, two reconstructed Ca layers on the top of a Pt4As8 layer, and disordered Ca layer on the top of Fe2As2 layer. The electronic properties of individual layers are studied using scanning tunneling microscopy/spectroscopy (STM/S), which reveals different spectra for each surface. Remarkably superconducting coherence peaks are seen only on the ordered Ca/Pt4As8 layer. Our results indicate that an ordered structure with proper charge balance is required in order to preserve superconductivity.

High pressure growth and electron transport properties of superconducting SmFeAsO1−xHx single crystals

“…The metallic conduction with a convex curvature of ρ ab (T) is similar to the polycrystalline case, while in contrast, the ρ c (T) behaves semiconducting. The resistivity anisotropy (ρ c /ρ ab ), reflecting the crystal and electronic structures of material, reaches 7.8 at T = 50 K. In Table 2 we summarize the ρ c /ρ ab at T = 50 K of several iron-based superconductors [23][24][25][26][27][28][29][30][31]. The slightly smaller ρ c /ρ ab in SmFeAsO 0.9 H 0.10 (ρ c /ρ ab = 7.8) than SmFeAsO 0.7 F 0.25 (ρ c /ρ ab = 8.4) may reflect an increased three dimensionality of the electronic structure in hydrogen-substituent proposed theoretically in CaFeAsH and CaFeAsF [32].…”

Atomically imaged crystal structure and normal-state properties of superconducting Ca10Pt4As8Wang1, Jin2, Tao3 et al. 2019Phys. Rev. BSelf Cite4110View full textAdd to dashboardCite

“…This means that the Pt 4 As 8 layer competes with neighboring negatively charged FeAs layer for electrons provided by Ca. As a result, atomic displacement and stoichiometry in Ca 10 Pt 4 As 8 (Fe 2 As 2 ) 5 is critical to both superconductivity and the normal-state physical properties [12,13]. Evidence is accumulating that subtle changes in either Ca or Pt distribution [12,14] or FeAs 4 tetrahedral distortion [13,14] would negatively impact superconductivity in Ca 10 Pt 4 As 8 (Fe 2 As 2 ) 5 .…”

“…As a result, atomic displacement and stoichiometry in Ca 10 Pt 4 As 8 (Fe 2 As 2 ) 5 is critical to both superconductivity and the normal-state physical properties [12,13]. Evidence is accumulating that subtle changes in either Ca or Pt distribution [12,14] or FeAs 4 tetrahedral distortion [13,14] would negatively impact superconductivity in Ca 10 Pt 4 As 8 (Fe 2 As 2 ) 5 . For example, Pt vacancies in Ca 10 Pt 3 As 8 (Fe 2 As 2 ) 5 leads to the absence of superconductivity [5][6][7].…”

Evidence for a preformed Cooper pair model in the pseudogap spectra of a Ca10(Pt4As8)(Fe2As2)5 single crystal with a nodal superconducting gap

“…In recent STM studies on Ca1048 compounds 31 , the SC gap size was observed to be approximately 35 cm −1 . This result is larger than the size of the SC gap of the Drude-2 band mentioned above, so it is judged to be the SC gap formed from the Drude-1 band.…”