Anomalous thermodynamic exponents from topological transitions in nodal superconductors

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• Dr. Jorge Quintanilla, University of Kent
• Thursday 14 November 2013, 13:45-15:00
• Theory Library.

If you have a question about this talk, please contact Kevin Ralley.

I will describe a simple generalisation of the theory of nodal quasiparticles and use it to derive a bulk thermodynamic signature of certain topological transitions. The theory of nodal quasiparticles has a wide range of applications, from unconventional superconductors to topological superconductors and graphene. At low temperatures, their linear dispersion away from a nodal point or line on the Fermi surface (a Dirac point or a Dirac line), leads to a characteristic power-law dependence of the specific heat:

In superconductors, such behaviour can be used to detect experimentally whether the order parameter has line nodes (n = 2) or point nodes (n = 3) and therefore to identify the Cooper pairing symmetry. I this talk I will show that other, non-integer exponents are possible. These occur when line nodes cross or near topological transitions where point nodes, line nodes, or line node crossings either appear, disappear or re-configure themselves in a non-trival way on the Fermi surface (e.g., at a line reconnection transition where the number of rings of line nodes on the Fermi surface changes). Such anomalous exponents thus provide bulk thermodynamic signatures of the topological transitions in question.

Interestingly, you don’t need to be exactly at the transition in order to observe the anomalous exponent – merely being near the transition is enough to observe the anomalous power law down to some characteristic temperature scale T* below which the more conventional behaviour is found – a behaviour strongly reminiscent of a quantum critical endpoint (QCEP).

[1] B. Mazidian, J. Quintanilla, A.D. Hillier, J.F. Annett, arXiv:1302.2161

This talk is part of the Theoretical Physics Seminars series.

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