Dataset Information

High-temperature superconductivity from fine-tuning of Fermi-surface singularities in iron oxypnictides.

ABSTRACT: In the family of the iron-based superconductors, the REFeAsO-type compounds (with RE being a rare-earth metal) exhibit the highest bulk superconducting transition temperatures (Tc) up to 55?K and thus hold the key to the elusive pairing mechanism. Recently, it has been demonstrated that the intrinsic electronic structure of SmFe0.92Co0.08AsO (Tc?=?18?K) is highly nontrivial and consists of multiple band-edge singularities in close proximity to the Fermi level. However, it remains unclear whether these singularities are generic to the REFeAsO-type materials and if so, whether their exact topology is responsible for the aforementioned record Tc. In this work, we use angle-resolved photoemission spectroscopy (ARPES) to investigate the inherent electronic structure of the NdFeAsO0.6F0.4 compound with a twice higher Tc?=?38?K. We find a similarly singular Fermi surface and further demonstrate that the dramatic enhancement of superconductivity in this compound correlates closely with the fine-tuning of one of the band-edge singularities to within a fraction of the superconducting energy gap ? below the Fermi level. Our results provide compelling evidence that the band-structure singularities near the Fermi level in the iron-based superconductors must be explicitly accounted for in any attempt to understand the mechanism of superconducting pairing in these materials.

SUBMITTER: Charnukha A

PROVIDER: S-EPMC4683369 | biostudies-literature | 2015 Dec

REPOSITORIES: biostudies-literature

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High-temperature superconductivity from fine-tuning of Fermi-surface singularities in iron oxypnictides.

Charnukha A A Evtushinsky D V DV Matt C E CE Xu N N Shi M M Büchner B B Zhigadlo N D ND Batlogg B B Borisenko S V SV

Scientific reports 20151218

In the family of the iron-based superconductors, the REFeAsO-type compounds (with RE being a rare-earth metal) exhibit the highest bulk superconducting transition temperatures (Tc) up to 55 K and thus hold the key to the elusive pairing mechanism. Recently, it has been demonstrated that the intrinsic electronic structure of SmFe0.92Co0.08AsO (Tc = 18 K) is highly nontrivial and consists of multiple band-edge singularities in close proximity to the Fermi level. However, it remains unclear whether ...[more]

PMID: 26678565

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Project description:Iron is one of most abundant environmental metal ions but is highly limited in organisms. It is an important metal ion as it facilitates various biological processes, including catalysis of metabolic enzymes and DNA biogenesis. In bacteria, the ferric uptake regulator (Fur) protein controls iron uptake by regulating genes coding for iron transporters in response to iron concentration. This iron response is ascribed to Fur's intrinsic affinity for iron because its binding to iron dictates its regulatory function. However, we now report that the pathogen Salmonella achieves a proper response of Fur to changes in environmental iron concentrations via EIIANtr (a nitrogen metabolic phosphotransferase system component). We establish that EIIANtr increases expression of iron transporter-coding genes under low-iron conditions (i.e., nanomolar ranges) in a Fur-dependent manner, which promotes Salmonella growth under such conditions. EIIANtr directly hampers Fur binding to DNA, thereby inducing expression of those genes. This regulation allows Salmonella to express Fur-regulated genes under low-iron conditions. Our findings reveal a potentially widespread control mechanism of bacterial iron uptake systems operating in response to iron availability.IMPORTANCE Iron is a fundamental metal ion for living organisms as it facilitates various biological processes. The ferric uptake regulator (Fur) protein controls iron homeostasis in various bacterial species. It is believed that Fur's iron-dependent regulatory action is sufficient for it to function as an iron sensor. However, we now establish that the bacterial pathogen Salmonella enables Fur to properly reflect changes in surrounding iron availability by fine-tuning its responsiveness to iron. This process requires a protein that hampers Fur DNA binding at low iron concentrations. In this way, Salmonella broadens the range of iron concentrations that Fur responds to. Our findings reveal a potentially widespread control mechanism of bacterial iron homeostasis.

Dataset Information

High-temperature superconductivity from fine-tuning of Fermi-surface singularities in iron oxypnictides.

Publications

High-temperature superconductivity from fine-tuning of Fermi-surface singularities in iron oxypnictides.

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