Dresden 2011 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 36: SC: Fe-based Superconductors - 122 - Properties, Electronic Structure, Mechanisms

TT 36.1: Talk

Wednesday, March 16, 2011, 14:00–14:15, HSZ 304

High-resolution thermal expansion of Ba(Fe_1−xCo_x)₂As₂: evidence for quantum criticality — •Christoph Meingast¹, Frederic Hardy¹, Philipp Burger^1,2, Devang Joshi¹, Peter Adelmann¹, Doris Ernst¹, Rainer Fromknecht¹, Peter Schweiss¹, Rolf Heid¹, and Thomas Wolf¹ — ¹Karlsruhe Institute of Technology, Institute for Solid State Physics, 76021 Karlsruhe, Germany — ²Karlsruhe Institute of Technology, Fakultät für Physik, 76128 Karlsruhe, Germany

Unconventional superconductivity is often found in the vicinity of a doping- or pressure-induced magnetic instability, or quantum phase transition (QPT). For a pressure-induced QPT, the Grüneisen parameter is expected to diverge as temperature approaches zero and is thus a very sensitive parameter for detecting a QPT. Experimentally, the Grüneisen parameter can be determined by the ratio of the thermal expansivity to the specific heat. Here we report on high-resolution thermal expansion and specific heat measurements of Ba(Fe_1−xCo_x)₂As₂ single crystals as a function of doping. We show that the electronic Grüneisen parameter exhibits all the features expected at a QPT: 1) non-Fermi-liquid behavior, 2) sign change of the Grüneisen parameter at the spin-density-wave transition, and 3) a divergences of the Grüneisen parameters at the beginning and end points of the superconducting dome.