Iron-based Superconductivity Research at the NCNR
| In 2008 a new class of high transition temperature (high-Tc) superconducting materials based on iron (Fe) and a “pnictide” (e.g., arsenic) was discovered, in which Fe-pnictide layers play a role analogous to the copper-oxygen planes in the high-Tc cuprates. An intense, world-wide competition is underway to understand and exploit these materials, and the NCNR is making leading contributions, both in experiment and theory. |
Most of the large, precise magnetic fields needed in MRI machines are provided by superconducting electromagnets cooled by liquid helium to very low temperatures. They are based on “low-Tc” materials like niobium-titanium alloys that were developed commercially 47 years ago. “High-Tc” materials, which superconduct at high enough temperatures that cheap liquid nitrogen can be used, were discovered in 1986. These materials are layered cuprate ceramics in which the dominant structural elements are planes of copper-oxygen. Yet, in spite of intensive science and engineering efforts, the cuprates have not become as useful as the low-Tc alloys.
High-Tc
superconductivity in the cuprates remains one of the great, unexplained
mysteries of condensed matter physics. The current belief is that the
magnetic moments (i.e., spins) of the copper ions play a major role in
cuprate superconductivity. High transition temperatures were also
thought to be unique to the cuprates, until the discovery of the
high-Tc Fe-pnictides.
The Fe-pnictides provide an entirely new window to high-Tc superconductivity. Combining state-of-the-art neutron scattering measurements with the predictive power of first-principles quantum mechanical calculations, the structure and properties of the Fe-pnictides have been shown to be extremely sensitive to the magnetic moment of the Fe ions, as predicted theoretically by NCNR’s Taner Yildirim, and measured using a variety of neutron instruments at the NCNR by our users, NIST scientists and their collaborators from around the US and worldwide.
Please follow the links below to their work.
http://www.ncnr.nist.gov/staff/jeff/IronSuperconductors.html
Key Role of Iron-Spin in High-Temperature Iron-Arsenic Superconductors
http://www.ncnr.nist.gov/staff/taner/highlights.htm
structural and magnetic properties