The Nernst response of mobile superconducting vortices, Kamran Behnia ESPCI/CNRS

seminaire hebdomadaire SMQ

Physique

Any solid hosting mobile charge carriers will produce an electric field in presence of a thermal gradient. This is a consequence of the combined conservation of energy and particle number. The Nernst effect refers to the off-diagonal component of this thermoelectric response emerging in presence of a finite magnetic field.

At the beginning of the present century, it was generally assumed that the quasi-particle contribution to the Nernst signal is negligible and a BCS superconductor cannot produce a Nernst signal far above its critical temperature. These assumptions were contradicted by subsequent experiments, which showed that the transverse thermoelectric response quantifies the amount of entropy bound to a mobile carrier of magnetic flux [1].

A recent surprise [2] is that the entropy carried by a mobile superconducting vortex is much smaller than what it stocks in its core. Available experimental data point to the universality of the mobile sheet entropy of a magnetic flux line across different superconductors with vastly different critical temperatures. This may be due to an information barrier surrounding the topological singularity of vortices in fermionic superfluids [3].
1. K. Behnia & H. Aubin, Rep. Prog. Phys. 79 (2016) 046502
2. C. W. Rischau et al., Phys. Rev. Lett. 126, 077001 (2021)
3. G. E. Volovik, The Universe in a Helium Droplet, Oxford (2003)