Dresden 2017 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 69: Focus Session: Superconductivity in the Vicinity of a Quantum Critical Point

TT 69.2: Hauptvortrag

Donnerstag, 23. März 2017, 15:30–16:00, HSZ 03

Quantum Criticality in Cuprate and Iron Based Superconductors — •Antony Carrington — University of Bristol, U.K.

I will review experiments which show that BaFe₂(As_1−xP_x)₂ is perhaps the best example of a quantum critical superconductor with a high T_c. Quantum oscillation cyclotron mass, specific heat and magnetic penetration depth are all strongly enhanced over a narrow range of x. Interestingly this increase in mass does not influence either the lower or upper critical fields in the expected way.

I will also discuss the applicability of quantum criticality to the cuprates. By measuring quantum oscillations in YBa₂Cu₄O₈ under hydrostatic pressure we are able to show that the quasiparticle mass decreases as maximum T_c is approached. This result is opposite to the behaviour found when YBa₂Cu₃O_7−δ is tuned towards maximum T_c by oxygen doping. Our results suggest that the proximity of the CDW end point to the maximum in T_c with doping is coincidental and that therefore quantum fluctuations of the CDW order do not boost T_c in the cuprates.