Pressure tuning of unconventional superconductors
(For a PhD PROJECT on pressure-tuning of electronic matter with focus on magnetism and superconductivity click here)
The search for superconductors with high transition temperatures continues to be a central theme of condensed-matter research. This is due to the high temperature superconductivity's potential for a wide range of applications as well as due to the fundamental questions of solid-state quantum theory associated with this state of electronic matter. The materials with the highest superconducting transition temperatures are the heavily studied Cuprates but despite a huge research effort, these materials and the mechanisms leading to the superconducting state have not yet been fully understood.
Recently, a novel class of Fe-based superconductors with relatively high transition temperatures has been discovered. The crystal structure contains a layered structure with similarities to the Cuprates. The CuO square lattice of the Cuprates is replaced by a Fe containing plane with tetrahedral coordination (see Figure for example BaFe2As2).
The new Fe-based class of superconductors allows to gain more insight in what are the key ingredients leading to high-temperature superconducting states. Magnetic interactions and structural properties may play an important role and recently, we have shown that not only the superconducting state but also the underlying magnetic phase of the parent compounds is highly sensitive to the type of structural changes.
To obtain a high success rate in scanning candidate materials for unconventional superconductivity, we tune their properties with high-pressure equipment in the large range between 0 and 200 kbar. We carry out electrical transport studies and have recently developed an extreme-conditions susceptometer for measurements of magnetic properties. We have established a collaboration with Diamond Light Source Ltd at Rutherford Appleton Laboratory on the Harwell Campus. Work on the extreme conditions beamline I15 will make powder diffraction studies up to high pressures and down to low temperatures possible.
 WJ Duncan, OP Welzel, C Harrison, X-H Chen, FM Grosche, PG Niklowitz, ”High pressure study of BaFe2As2 – the role of hydrostaticity and uniaxial stress”, J. Phys.: Condens. Matter 22 (2010) 052201 (IoP Select)