Séminaire de Physique Théorique
Thermoelectric signatures of superconducting states that break time-reversal symmetry (Salle E1100)Julien Garaud (Royal Inst. Tech., Stockholm & Massachusetts U.)
Thursday 22 October 2015 14:00 - Tours - Salle à préciser
Résumé :
There have been recently large interest in superconducting states that break time-reversal symmetry. This interest is sparked by iron-based superconductors where pairing is supposed to take place in several sheets of a Fermi surface and where several pairing channels may compete. In pnictides, and in particular in hole doped Ba$_{1-x}$K$_x$Fe$_2$As$_2$, two alternative scenario for TRSB states are considered, namely $s+is$ and $s+id$ states [1-3]. These feature mixed contribution of various pairing channels, and there the time-reversal symmetry breaking (TRSB) states, are characterized by relative phases of the gaps on different pockets that differ by less than $\pi$. Probing such relative phases between the gaps is a very non-trivial task [3]. More than 70 years ago, Ginzburg [4,5] pointed out that superconductors feature thermoelectric effects originating in a charge transfer by thermal quasi-particles which is compensated by a counterflow of supercurrents. I will demonstrate that, as a consequence of the modified London's electrodynamics in multi-band superconductors, there appears a new contribution to the thermally induced supercurrent [6]. In TRSB states that contribution can be orders of magnitude larger than that of the ordinary Ginzburg's mechanism [4,5] and in contrast be present even at low temperatures. Finally I will present possible measurements, relying on these unconventional thermoelectric properties of TRSB states, that should provide direct informations about the underlying pairing mechanism (either $s+is$ or $s+id$ states) of iron-based superconductors [7]. [1] S. Maiti, A. V. Chubukov; Phys. Rev. B 87, 144511 (2013) [2] S. Maiti, M. Sigrist, A. V. Chubukov; Phys. Rev. B 91, 161102 (2015) [3] M. Marciani, L. Fanfarillo, C. Castellani, L. Benfatto; Phys. Rev. B 88, 214508 (2013). [4] V. L. Ginzburg; Zhurnal Eksperimentalnoi i Teoreticheskoi Fiziki 14, 177 (1944). [5] V. L. Ginzburg, G. F. Zharkov; Soviet Physics Uspekhi, 21, 381 (1978). [6] M. Silaev, J. Garaud, E. Babaev; arXiv:1503.02024 [7] J. Garaud, M. Silaev, E. Babaev; arXiv:1507.04712
Liens :