PHYSICS SEMINAR
THERMOELECTRIC PROPERTIES OF HIGH Tc SUPERCONDUCTORS
Paul Calvert
Physics Department
Bishop’s University
Friday, February 18, 2011
1:30-2:30 p.m.
Nicolls 315
In 1911, three years after helium was first liquefied, it was discovered experimentally that the electrical resistivity of many metals vanishes below a phase transition at a low finite temperature (Tc). Not until 1933 did Meissner and Ochsenfeld discover that these materials act as pure diamagnets in this phase. In 1957 Bardeen, Cooper and Schrieffer finally published the “BCS theory of superconductivity”, which successfully explained most properties through “Cooper pairing”. The highest Tc known was 23 K for most of the 20th century. This dramatically changed in 1986 with the discovery of superconductivity in hole-doped cuprates, and the record Tc was 125 K by 1988, well above the boiling point of nitrogen and almost halfway to room temperature. Despite intense research into this class of metals, the origin of superconductivity in the cuprates is still not fully understood. Is the pairing due to electron-lattice interactions or is it purely electronic in nature? What is the nature of the pseudogap? Is it a real phase or a precursor to superconductivity? What is the role of a possible Quantum Critical Point? Then in 2008 a new class of iron-pnictide high Tc superconductors, with a phase diagram remarkably similar to that of the cuprates, was discovered. Were the mechanisms leading to superconductivity the same as that in the cuprates? My research explores the thermoelectric properties of FeCrAs, a non-superconducting iron-pnictide, to explore a possible Fermi surface reconstruction and its relation to antiferromagnetic ordering.
