Normal and superconducting state electronic structure of iron based superconductors
Lead Research Organisation:
University of Bristol
Department Name: Physics
Abstract
Superconductivity is a fascinating phenomenon giving rise to quantum coherence over vast distances (several hundred kilometres of wire). It also has many valuable practical applications - basically anything which uses electricity can in principle benefit from superconducting technology. The most obvious applications are lossless power transmission cables, very high efficiency power transformers and generators. These applications have been promised since the early days of superconductivity at the start of the 20th century, but are only now becoming practical 20 years after the discovery of materials which superconduct above the boiling point of liquid nitrogen (77 Kelvin). The discovery and refinement of new superconducting materials benefits immensely from improving our understanding of their fundamental physics - most importantly the reason for the formation of the coherent superconducting state. Despite more than twenty years of research there is still no consensus as to the mechanism of high temperature superconductivity in the famous copper oxide (cuprate) materials. The discovery just over one year ago of high temperature superconductivity in material containing the element iron was very surprising as the magnetism normally associated with iron is highly detrimental to the formation of the superconducting state. These materials are of great interest from a point of view of both the fundamental physics and potential applications. The former stems from several key similarities (and differences) with the cuprate superconductors - perhaps making these materials the 'Rosetta stone' that can be used to understand how electronic mechanisms can produce a high temperature superconducting state. The latter from the fact that some materials continue to superconduct even when subjected to the world most intense magnetic fields in excess of 60T.The research in this proposal aims to further our understanding of high temperature superconductivity and in particular iron-based superconductors by pursuing two related research paths. One path will address the nature of the superconductivity itself. By measuring the influence of temperature on the density of superconducting electrons, through measurement of properties such as the magnetic penetration depth (i.e., the fundamental ability of a superconductor to screen out an applied magnetic field) we can learn the microscopic properties of the electrons which carry the superconducting current. The other path will be to study the properties of the 'normal' metal state. By applying large magnetic field, the superconductivity can be suppressed (effectively turned off) and then we can study the non-superconducting normal metallic state of the materials. In sufficiently high field, characteristic periodic oscillations of the magnetisation as a function of field (the de Haas-van Alphen effect) reveal the exact momenta of the electrons that carry current and how this momentum varies as a function of direction. This determination of the 'electronic structure' of a metal is akin to knowing its DNA. By studying how this normal state electronic structure varies in the different materials and how this influences the superconducting properties it will be possible to build up a theoretical picture of the mechanism of high temperature superconductivity.
Planned Impact
As this is essentially fundamental research the economic benefit will likely be in the medium to long term (5 - 20 years). As this field is very new (around 1 year old) the timescale for applications is presently unknown as it depends strongly on the detailed properties of these newly discovered materials which are only just now being explored. Understanding of the fundamental principles of superconductivity will be of benefit to technologists working to develop application of superconductors. The economic impact of superconductivity has been predicted to increase significantly in the first few decades of the 21st century. Its progress is critically dependent on improvements in the characteristics of the materials, which goes hand-in-hand with improved understanding of their fundamental properties. A more immediate benefit of the research is the training of the post-doc and student associated with the project. The experimental and analytical skills learn will be of benefit to a wide section of UK industry. In particular, several UK companies (e.g., Siemens magnet technology / Oxford Instruments) have a direct need for graduates with a strong background in experimental physics at cryogenic temperature and high magnetic fields.
Organisations
People |
ORCID iD |
Antony Carrington (Principal Investigator) |
Publications
Shibauchi T
(2014)
A Quantum Critical Point Lying Beneath the Superconducting Dome in Iron Pnictides
in Annual Review of Condensed Matter Physics
Coldea A
(2013)
Iron-based superconductors in high magnetic fields
in Comptes Rendus Physique
Carrington A
(2011)
Studies of the gap structure of iron-based superconductors using magnetic penetration depth
in Comptes Rendus Physique
Putzke C
(2014)
Anomalous critical fields in quantum critical superconductors.
in Nature communications
Wilcox JA
(2022)
Observation of the non-linear Meissner effect.
in Nature communications
Hashimoto K
(2010)
Evidence for superconducting gap nodes in the zone-centered hole bands of KFe 2 As 2 from magnetic penetration-depth measurements
in Physical Review B
Serafin A
(2010)
Anisotropic fluctuations and quasiparticle excitations in FeSe 0.5 Te 0.5
in Physical Review B
Coldea A
(2014)
Cascade of field-induced magnetic transitions in a frustrated antiferromagnetic metal
in Physical Review B
Hashimoto K
(2010)
Line nodes in the energy gap of superconducting BaFe 2 ( As 1 - x P x ) 2 single crystals as seen via penetration depth and thermal conductivity
in Physical Review B
Arnold B
(2011)
Nesting of electron and hole Fermi surfaces in nonsuperconducting BaFe 2 P 2
in Physical Review B
Putzke C
(2012)
de Haas-van Alphen study of the Fermi surfaces of superconducting LiFeP and LiFeAs.
in Physical review letters
Hashimoto K
(2012)
Nodal versus nodeless behaviors of the order parameters of LiFeP and LiFeAs superconductors from magnetic penetration-depth measurements.
in Physical review letters
Mercure JF
(2012)
Upper critical magnetic field far above the paramagnetic pair-breaking limit of superconducting one-dimensional Li0:9Mo6O17 single crystals.
in Physical review letters
Walmsley P
(2013)
Quasiparticle mass enhancement close to the quantum critical point in BaFe2(As(1-x)P(x))2.
in Physical review letters
Hashimoto K
(2013)
Anomalous superfluid density in quantum critical superconductors.
in Proceedings of the National Academy of Sciences of the United States of America
Carrington A
(2011)
Quantum oscillation studies of the Fermi surface of iron-pnictide superconductors
in Reports on Progress in Physics
Hashimoto K
(2012)
A sharp peak of the zero-temperature penetration depth at optimal composition in BaFe2(As(1-x)P(x))2.
in Science (New York, N.Y.)
Wilcox J
(2020)
Observation of the Non-linear Meissner Effect
Wilcox J
(2022)
Observation of the non-linear Meissner effect
Description | This work was basic fundamental research into the recently discovered iron-based high temperature superconductors. The goals were to investigate the normal state and superconducting state electronic structure of these materials. The purpose of this research is to move towards a better understanding of the fundamental theory of high temperature superconductivity with a view to being able to better exploit these materials for applications in fields such as energy transmission or healthcare (MRI scanners). The most notable outcomes were as follows: 1) Established that the structure of the superconducting energy gap in iron-based superconductors in non-universal. Unlike cuprate superconductors, the gap structure depends critically on the details of the interaction which causes the superconductivity. Hence, this suggests that the gap structure can be used as a unique highly sensitive test of candidate microscopic theories. 2) Determined the topology of the Fermi surface and the properties of the low energy quasiparticles in the normal state of a number of different iron-pnctides, such as LaFePO, LiFeP and BaFe2(As1-xPx)2. This ties in to (1) above and can be used by theorist as an input to microscopic calculations of superconductivity using candidate interactions 3) Established the nature of the quantum critical point, where superconductivity has the maximum Tc in BaFe2(As1-xPx)2. In particular, we showed that there is a peak in the quasiparticle mass in the superconducting state, and hence that in this material the quantum critical point is not 'avoided'. 4) Established the behaviour of the critical fields of BaFe2(As1-xPx)2 near its quantum critical point. Fluctuations around an antiferromagnetic quantum critical point (QCP) are believed to lead to unconventional superconductivity and in some cases to high-temperature superconductivity. However, the exact mechanism by which this occurs remains poorly understood. The iron-pnictide superconductor BaFe2(As1-xPx)2 is perhaps the clearest example to date of a high temperature quantum critical superconductor, and so it is a particularly suitable system in which to study how the quantum critical fluctuations affect the superconducting state. We showed that the proximity of the QCP yields unexpected anomalies in the superconducting critical fields. We find that both the lower and upper critical fields do not follow the behaviour, predicted by conventional theory, resulting from the observed mass enhancement near the QCP. Our results imply that the energy of superconducting vortices is enhanced, possibly due to a microscopic mixing of antiferromagnetism and superconductivity, suggesting that a highly unusual vortex state is realised in quantum critical superconductors. |
Exploitation Route | This is fundamental research and so the immediate beneficiaries are academic. The work has been published in high impact journals (Science, Physical Review Letters) and has received a high number of citations already. The impact is on the immediate field of iron-based superconductors and also on the wider field of high temperature superconductivity - particularly it advances our understanding of cuprate high temperature superconductivity and the behaviour of material close to quantum critical points. Non-academic impact will be limited at present, but the eventual goal of understanding and controlling high temperature superconductivity will have wide and far reaching impacts in all areas of technology which depend on electronics or electrical transport. |
Sectors | Energy,Healthcare |
Description | Intra-European Marie Curie Research Fellowship |
Amount | € 142,000 (EUR) |
Funding ID | FESUME |
Organisation | European Research Council (ERC) |
Sector | Public |
Country | Belgium |
Start | 06/2011 |
End | 06/2013 |
Description | Standard Research |
Amount | £496,658 (GBP) |
Funding ID | EP/L025736/1 |
Organisation | Engineering and Physical Sciences Research Council (EPSRC) |
Sector | Public |
Country | United Kingdom |
Start | 12/2014 |
End | 12/2017 |