Probing the Superfluid Stiffness of Superconducting Arsenides

Lead Research Organisation: University of Oxford
Department Name: Oxford Physics

Abstract

Superconductivity was discovered in 1911 and started to become useful in applications only in the 1960's. High-temperature superconductivity in copper-containing compounds was discovered in the mid-1980s and raised the prospect of more useful devices utilising superconductivity. Early in 2008, another breakthrough was achieved: very new materials were discovered containing iron (a surprise since magnetic iron was previously thought to be exactly the sort of atom you would not wish to include in a superconductor!) and these have provided an enormous and urgent stimulus to research since the origin of this effect is unknown. Using a combination of synthetic chemistry (an approach which has led to new superconductors being discovered in Oxford in the last few months), high-resolution structural measurements (using neutrons and x-rays) and probes of superfluid stiffness (using muons) we have devised a strategy to provide unique information about these new compounds which we believe will be critical to understanding the mechanism in this fascinating new family of materials.

Publications

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Burrard-Lucas M (2013) Enhancement of the superconducting transition temperature of FeSe by intercalation of a molecular spacer layer. in Nature materials

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Ghannadzadeh S (2014) Upper critical field of NaFe 1 - x Co x As superconductors in Physical Review B

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Pitcher MJ (2010) Compositional control of the superconducting properties of LiFeAs. in Journal of the American Chemical Society

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Sun H (2015) Soft chemical control of superconductivity in lithium iron selenide hydroxides Li(1-x)Fe(x)(OH)Fe(1-y)Se. in Inorganic chemistry

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Wright J (2013) Magnetic fluctuations and spin freezing in nonsuperconducting LiFeAs derivatives in Physical Review B

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Wright J (2012) Gradual destruction of magnetism in the superconducting family NaFe 1 - x Co x As in Physical Review B

 
Description The very recent discovery of in FeAs-based compounds has provided an opportunity to make huge strides in understanding superconductivity. Our aim was to understand this newly discovered FeAs-based superconductivity by detailed structural, magnetic and superconducting characterization using a combination of lab-based (magnetometry and heat capacity) and facility-based (neutron and muon) techniques. We wanted to (i) progress materials discovery via identified synthetic strategies, (ii) correlate detailed structural information with measurements of superfluid stiffness and (iii) test for coexistence of magnetism and superconductivity.The results of this work were to achieve these objectives, as stated in the grant proposal, and have led to a new understanding of Co-doped NaFeAs superconductors. The superconducting phase diagram was determined and the relationship with the magnetic state mapped out in detail.
Exploitation Route The review article on ac susceptibility (Topping and Blundell, 2019), which was a product of the thesis work, is likely to be highly influential in the field. The work clarifying the nature of the spin glass state of Li1-xFex(OH)Fe1-ySe was presented at the APS March Meeting 2019 and will lead to impact in this area. The development work done on the Oxford pulsed field system will be taken forward by the Oxford group and will have wide impact in a number of science areas.
Sectors Energy
URL http://correlated.physics.ox.ac.uk/
 
Description Soft chemical control to achieve new layered architectures and strongly correlated states.
Amount £556,382 (GBP)
Funding ID EP/P018874/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 05/2017 
End 05/2020