Superconductivity and low temperature annealing of Ca122: neither P1 nor P2 phase is superconducting; P1 phase can be turned into P2 phase continuously by low temperature annealing at 350 C; superconductivity occurs with a constant onset temperaure Tco over a narrow annealing time window and with a time-dependent superconducting volume fraction f.
Superconductivity and low temperature annealing of Ca122: neither P1 nor P2 phase is superconducting; P1 phase can be turned into P2 phase continuously by low temperature annealing at 350 C; superconductivity occurs with a constant onset temperaure Tco over a narrow annealing time window and with a time-dependent superconducting volume fraction f.
“Our results show that indeed interfaces can induce superconductivity above 25K in non-superconducting CaFe2As2, showing a new path to high Tc is possible”Paul Chu

Research by scientists at the University of Houston has shown how to induce superconductivity in non-superconducting materials, as well as increasing the efficiency in known superconducting materials, a breakthrough that could promote the practical viability of superconductors.

Superconductivity already benefits areas such as MRI and healthcare, but remains an expensive option, partly due to the cost of cooling. However, superconducting materials conduct electric current without resistance, as opposed to traditional transmission materials that can lose up to 10% of energy between the generating source and the end-user. This property could lead to superconductors being used by utility companies to generate more electricity without the need to raise the amount of fuel used.

While the idea of inducing superconductivity at the interface of two different materials has been around since the 1960s, and was even then able to show enhanced superconducting at critical temperatures (Tc), this is the first time it has been demonstrated effectively without other effects such as stress or chemical doping becoming factors.

The approach to achieving enhanced Tcs, the temperature at which a material becomes superconducting, using artificially or naturally assembled interfaces was the basis of this new study, which was published in the journal Proceedings of the National Academy of Sciences [Zhaio et. al. Proc. Natl. Acad. Sci. USA (2016) DOI: 10.1073/pnas.1616264113]. It proposes a technique for using assembled interfaces to induce superconductivity in the well-known non-superconducting compound calcium iron arsenide through antiferromagnetic/metallic layer stacking, offering the best evidence so far for the interface-enhanced Tc in this compound.

To validate the concept, in ambient pressure the team exposed the undoped calcium iron arsenide compound to heat of 3500C, seen as quite low for the process, in a procedure known as annealing. The compound formed two distinct phases – one phase increasingly converted to the other for the longer the sample was annealed. Although neither of the phases was superconducting, they could detect superconductivity at the point where the two phases coexist.

While the superconducting critical temperature of the sample was relatively low, the technique used could present a new approach to identifying more efficient and cheaper superconducting materials. As corresponding author Paul Chu pointed out, “Our results show that indeed interfaces can induce superconductivity above 25 K in non-superconducting CaFe2As2, showing a new path to high Tc is possible”. The team is now looking to develop robust materials with practically high Tc and critical current density (Jc) following this route for applications.