Dresden 2014 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 53: Superconductivity: Fe-based Superconductors - 122

TT 53.3: Talk

Wednesday, April 2, 2014, 10:00–10:15, HSZ 201

Superconducting specific heat jump Δ C ∝ T_c^β (β ∼ 2) and gapless Fermi surfaces in K_1−xNa_xFe₂As₂ — •V. Grinenko¹, D.V. Efremov¹, S.-L. Drechsler¹, S. Aswartham¹, D. Gruner¹, M. Roslova¹, I. Morozov¹, K. Nenkov¹, S. Wurmehl^1,2, A.U.B. Wolter¹, B. Holzapfel^1,3, and B. Büchner^1,2 — ¹Leibniz-Institute for Solid State and Materials Research, IFW-Dresden, D-01171 Dresden, Germany — ²Institut für Festkörperphysik, TU Dresden, Germany — ³Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany

We present a systematic study of the electronic specific heat jump (Δ C_el) at the superconducting transition temperature T_c of K_1−xNa_xFe₂As₂. Both T_c and Δ C_el monotonously decrease with increasing x. The jump scales approximately with a novel power-law: Δ C_el ∝ T_c^β with β ≈ 2 determined by the impurity scattering rate. This finding is in sharp contrast to most of all iron-pnictide superconductors with a cubic Bud’ko-Ni-Canfield (BNC) scaling. Our observations, also, suggests that disorder diminishes the small gaps leading to partial gapless superconductivity which results in a large residual Sommerfeld coefficient in the superconducting state for x > 0. Both T-dependence of C_el(T) in the superconducting state and the nearly quadratic scaling of Δ C_el at T_c are well described by the Eliashberg-theory for a single-band d-wave superconductor with weak pair-breaking due to nonmagnetic impurities having reduced the density of superconducting quasi-particles.