C. Putzke

Jeudi 20 Octobre 2016 14h
Amphi Holweck, Esc C
1ème etage

High-temperature superconductivity : A quantum
critical phenomena ?

C. Putzke
1 H.H. Wills Physics Laboratory, University of Bristol, Bristol, UK
In recent years the iron-pnictide BaFe2(As1-xPx)2 has been established as
the cleanest and clearest example in which to study the influence of
quantum critical fluctuations on high temperature superconductivity. The
observation of a sharp peak in the penetration depth at the quantum
critical point (QCP x=0.3) coincides with the maximum Tc [1]. Specific
heat and de Haas-van Alphen effect measurements [2] show that this
peak is driven by a corresponding increase in the quasiparticle effective
mass. The agreement of these different probes demonstrate the
influence of the QCP on superconductivity.
Based on these previous results a simple one-band theory would suggest
that at the QCP we expect a large increase in Hc2. Measurements of the
upper critical field however show a quite different behaviour.
The new inside into quantum critical superconductivity gained from the
iron-based superconductors has led us to revisit the quantum critical
scenarios proposed in the CuO-based high-temperature superconductors.
Here a strong quasiparticle mass-enhancement [3] together with strong
peaks Hc2 [4] were interpreted as indications for quantum critical
superconductivity. We have carried out Shubnikov-de Haas
measurements on the stoichiometric high-Tc YBa2Cu4O8 under hydrostatic
pressure. The results show a distinct different correlation of the
quasiparticle mass and superconductivity under pressure compared to
doping. This has important implications for our understanding of the
interplay between the charge density wave and superconductivity in the
[1] : K. Hashimoto, et al. Science 336, 1554 (2013)
[2] : P. Walmsley, et al. PRL 110, 257002 (2013)
[3] : B.J. Ramshaw, et al. Science 348, 317 (2015)
[4] : G. Grissonnanche, et al. Nat. Commun. 5, 3280 (2014)

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