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Abstract
Thermal conductivity, point contact spectroscopy, angle-resolved photoemission and Raman spectroscopy measurements were performed on BaFe1.9Pt0.1As2 single crystals obtained from the same synthesis batch in order to investigate the superconducting energy gap structure using multiple techniques. Low temperature thermal conductivity was measured in the superconducting state as a function of temperature and magnetic field, revealing an absence of quasiparticle excitations in the limit up to 15 T applied magnetic fields. Point-contact Andreev reflection spectroscopy measurements were performed as a function of temperature using the needle-anvil technique, yielding features in the conductance spectra at both 2.5 meV and 7.0 meV scales consistent with a multi-gap scenario. Angle-resolved photoemission spectroscopy probed the electronic band structure above and below the superconducting transition temperature of Tc = 23 K, revealing an isotropic gap of magnitude meV on both electron and hole pockets. Finally, Raman spectroscopy was used to probe quasiparticle excitations in multiple channels, showing a threshold energy scale of 3 meV below Tc. Overall, we find strong evidence for an isotropic gap structure with no nodes or deep minima in this system, with a 3 meV magnitude gap consistently observed and a second, larger gap suggested by point-contact spectroscopy measurements. We discuss the implications that the combination of these results reveal about the superconducting order parameter in the BaFe2−xPtxAs2 doping system and how this relates to similar substituted iron pnictides.
Highlights
Since their discovery,[1] the nature of the superconducting gap structure and pairing symmetry of ironbased superconductors (FeSCs) have attracted considerable attention.[2]
Thermal conductivity, point contact spectroscopy, angle-resolved photoemission and Raman spectroscopy measurements were performed on BaFe1.9Pt0.1As2 single crystals obtained from the same synthesis batch in order to investigate the superconducting energy gap structure using multiple techniques
We find strong evidence for an isotropic gap structure with no nodes or deep minima in this system, with a 3 meV magnitude gap consistently observed and a second, larger gap suggested by point contact spectroscopy measurements
Summary
Single crystals of BaFe1.9Pt0.1As2 were grown from prereacted FeAs and PtAs powders and elemental Ba using the FeAs self-flux method[22], which yielded large crystals with typical dimensions 0.1 × 1 × 2 mm[3] (Ref. 3). Single crystal x-ray diffraction and Rietveld refinement determined a precise Fe:Pt ratio and an exact chemical formula of BaFe1.906(8)Pt0.094(8)As2. Previous x-ray measurements have shown that Pt substitution reduces the c-axis length and c/a ratio while increasing the a-axis length and unit cell volume compared to pure BaFe2As2 (Ref. 3). Previous specific heat measurements[3] have confirmed the bulk nature of the transition, with a jump in Cp(T ) that occurs slightly below Tc. The size of the jump was estimated as ∆Cp/Tc ≈ 20 mJ mol−1K−1, and assuming the BCS weak-coupling ratio of ∆Cp/γTc =1.43 applies yields a value for γ = 16(2) mJ mol−1K−2.3
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