Wang, J.-H. | Search NASA

DOE OSTI2020

Orbital selectivity of layer-resolved tunneling in the iron-based superconductor Ba 0.6 K 0.4 Fe 2 As 2

Here, we use scanning tunneling microscopy/spectroscopy to elucidate the Cooper pairing of the iron pnictide superconductor Ba 0.6 K 0.4 Fe 2 As 2 . By a cold-cleaving technique, we obtain atomically resolved termination surfaces with different layer identities. Remarkably, we observe that the low-energy tunneling spectrum related to superconductivity has an unprecedented dependence on the layer identity. By cross referencing with the angle-revolved photoemission results and the tunneling data of LiFeAs, we find that tunneling on each termination surface probes superconductivity through selecting distinct Fe-3$\textit{d}$ orbitals. These findings imply the real-space orbital features of the Cooper pairing in the iron pnictide superconductors, and propose a general concept that, for complex multiorbital material, tunneling on different terminating layers can feature orbital selectivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

NASA NTRS2016

Payload Hardware and Experimental Protocol for Testing the Effect of Space Microgravity on the Resistance to Gentamicin of Stationary-Phase Uropathogenic Escherichia Coli and Its Sigma (sup S)-Deficient Mutant

Human immune response is compromised and bacteria can become more antibiotic resistant in space microgravity (MG). We report that under low-shear modeled microgravity (LSMMG) stationary-phase uropathogenic Escherichia coli (UPEC) become more resistant to gentamicin (Gm). UPEC causes urinary tract infections (UTIs), reported to afflict astronauts; Gm is a standard treatment, so these findings could impact astronaut health. Because LSMMG has been shown to differ from MG, we report here preparations to examine UPEC's Gm sensitivity during spaceflight using the E. coli Anti-Microbial Satellite (EcAMSat) on a free flying nanosatellite in low Earth orbit. Within EcAMSats payload, a 48-microwell fluidic card contains and supports study of bacterial cultures at constant temperature; optical absorbance changes in cell suspensions are made at three wavelengths for each microwell and a fluid-delivery system provides growth medium and predefined Gm concentrations. Performance characterization is reported for spaceflight prototypes of this payload system. Using conventional microtiter plates, we show that Alamar Blue (AB) absorbance changes due to cellular metabolism accurately reflect E. coli viability changes: measuring AB absorbance onboard EcAMSat will enable telemetry of spaceflight data to Earth. Laboratory results using payload prototypes are consistent with wellplate and flask findings of differential sensitivity of UPEC and its delta rpoS strain to Gm. Space MG studies using EcAMSat should clarify inconsistencies from previous space experiments on bacterial antibiotic sensitivity. Further, if sigma (sup s) plays the same role in space MG as in LSMMG and Earth gravity, EcAMSat results would facilitate utilizing our previously developed terrestrial UTI countermeasures in astronauts.

Matin, A. C.↗