Revealing the intrinsic superconducting gap anisotropy in surface-neutralized BaFe2(As0.7P0.3)2

Alkaline-earth iron arsenide (122) is one of the most studied families of iron-based superconductors, especially for angle-resolved photoemission spectroscopy. While extensive photoemission results have been obtained, the surface complexity of 122 caused by its charge-non-neutral surface is rarely considered. Here, we show that the surface of 122 can be neutralized by potassium deposition. In potassium-coated BaFe2(As0.7P0.3)2, the surface-induced spectral broadening is strongly suppressed, and hence the coherent spectra that reflect the intrinsic bulk electronic state recover. This enables the measuring of superconducting gap with unpreceded precision. The result shows the existence of two pairing channels. While the gap anisotropy on the outer hole/electron pockets can be well fitted using an s± gap function, the gap anisotropy on the inner hole/electron shows a clear deviation. Our results provide quantitative constraints for refining theoretical models and also demonstrate an experimental method for revealing the intrinsic electronic properties of 122 in future studies.

Revealing the intrinsic superconducting gap anisotropy in surface-neutralized BaFe2(As0.7P0.3)2

Alkaline-earth iron arsenide (122) is one of the most studied families of iron-based superconductors, especially for angle-resolved photoemission spectroscopy. Extensive results have been obtained including band structure, gap anisotropy, etc. However, the complicacy of 122 caused by its charge-non-neutral cleavage surface is rarely considered. Here, we show that the surface of 122 can be neutralized by potassium deposition. In potassium-coated BaFe2(As0.7P0.3)2, the surface-induced spectral broadening is strongly suppressed, while the coherent spectra that reflects the intrinsic bulk electronic state recovers. This raises the accuracy of the gap measurement and gap fitting to an unpreceded level. The results clearly distinguish two pairing channels originated respectively from the inner and outer Fermi pockets. While the gap anisotropy on the outer hole/electron pockets can be well fitted using an s± gap function, the gap magnitude on the inner hole/electron pockets show a clear deviation. Our results provide quantitative constraints for refining theoretical models and demonstrate an experimental method for revealing the intrinsic electronic properties of 122 in future studies.

Enhanced surface binding energy regulates uniform potassium deposition for stable potassium metal anodes

A SnO2-coated carbon fiber mat is fabricated and used to guide uniform K nucleation/deposition for dendrite free K metal anodes.

Electronic And Structural Properties Of Interfaces Created By Potassium Deposition ON TiO2 (110) Surfaces

ABSTRACTPotassium was deposited onto stoichiometric TiO2 (110) surfaces and the chemical bonding and structure were studied with UPS, XPS, LEED, and RHEED. Potassium interacts strongly with the oxygen anions of the TiO2 and reduces the valency of Ti cations at the interface. At submonolayer potassium coverages, a large charge transfer to the substrate causes a sharp drop in work function, a population of electronic states within the bulk TiO2 band gap, and surface band bending. After large potassium doses at 300 K, multilayers of K2O are formed by diffusion of oxygen anions from the substrate, creating a substoichiometric TiO2−x interface composition. No metallic potassium is present even after large doses. The K2O layers remain stable after annealing as high as 900 K, and LEED indicates that they are disordered. RHEED characterization is limited by the roughness of the stoichiometric TiO2 (110) surface.