Using four different experimental techniques, we performed comprehensive studies of the bulk superconductive properties of single crystals of the nearly optimally doped Ba1−xKxFe2As2 (Tc≈36K), a typical representative of the 122 family. We investigated temperature dependencies of the (i) specific heat Cel(T), (ii) first critical magnetic field Hc1(T), (iii) intrinsic multiple Andreev reflection effect (IMARE), and (iv) infrared reflectivity spectra. All data clearly show the presence of (at least) two superconducting nodeless gaps. The quantitative data on the superconducting spectrum obtained by four different techniques are consistent with each other: (a) the small energy gap ΔS(0)≈1.8−2.5meV, and the large gap energy ΔL(0)≈9.5−11.3meV that demonstrates the signature of an extended s-wave symmetry (∼33% in-plane anisotropy), (b) the characteristic ratio 2ΔL/kBTC noticeably exceeds the BCS value.
@article{arxiv.1612.05540,
title = {Probing Bulk Superconducting Order Parameter in Ba(K)Fe$_2$As$_2$ by Four Complementary Techniques},
author = {A. V. Muratov and T. E. Kuzmicheva and A. V. Sadakov and S. Yu. Gavrilkin and D. A. Knyazev and S. A. Kuzmichev and Yu. A. Aleshchenko and A. A. Kordyuk and V. M. Pudalov and M. Abdel-Hafiez},
journal= {arXiv preprint arXiv:1612.05540},
year = {2017}
}