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Louis TAILLEFER - Université de Sherbrooke

Pairing symmetry in the iron-based superconductor KFe2As2

The advent of iron-based superconductors in 2008 has revolutionized the field of high-temperature superconductivity. The pairing mechanism responsible for the robust superconductivity of these materials is still a matter of strong debate.

I will present our experimental studies of the iron-based superconductor KFe2As2. We have found a sudden reversal in the pressure dependence of its critical temperature Tc, producing a V-shaped temperature-pressure phase diagram, which we interpret in terms of a change of pairing state across the critical pressure [1,2]. At ambient pressure, our studies of the gap structure using thermal conductivity lead us to conclude that the pairing state is d-wave [3]. This implies that the pairing symmetry in the archetypal series Ba1-xKxFe2As2 changes from s-wave at optimal doping (x = 0.4) to d-wave at full doping (x = 1.0) [4].

These findings provide a new avenue for investigating the nature of the pairing mechanism in iron-based superconductors via this change of pairing symmetry.

[1] F. F. Tafti et al., Nature Physics 9, 349 (2013).

[2] F. F. Tafti et al., Physical Review B 89, 134502 (2014).

[3] J.-Ph. Reid et al., Physical Review Letters 109, 087001 (2012).

[4] J.-Ph. Reid et al., Superconductor Sience and Technology 25, 084013 (2012).