Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
1819125 | Physica C: Superconductivity and its Applications | 2009 | 7 Pages |
Abstract
We present specific heat measurements on single crystals of the pnictide superconductors NdFeAsO1âxFx and Ba1âxKxFe2As2. Low-temperature measurements on Ba1âxKxFe2As2 reveal that the Sommerfeld coefficient of the quasiparticle specific heat increases linearly with applied magnetic field. This is the signature of a fully gapped superconducting state as is expected for instance in the extended s-wave scenario. The large value of the normal state Sommerfeld coefficient indicates a large electronic density of states and significant mass enhancements. We determine the phase diagram using an entropy conserving construction, which does not require the choice of a resistivity criterion to define the transition temperature. Both materials display clear mean-field steps in the specific heat at Tc of 47 K and 34.6 K, respectively, proving bulk superconductivity. They are characterized by a low superconducting anisotropy near Tc of Πâ¼Â 4 for NdFeAsO1âxFx and 2.6 for Ba1âxKxFe2As2, which is promising for potential applications. We observe extraordinarily high upper critical field slopes of μ0âHc2c/âT=-6.5T/K and μ0âHc2ab/âT=-17.4T/K for Ba1âxKxFe2As2 which points to the emergence of paramagnetic limiting effects at low temperatures. A thermodynamic analysis reveals that this material is extreme type-II with κc â¼Â 100 and κab â¼Â 260.
Related Topics
Physical Sciences and Engineering
Physics and Astronomy
Condensed Matter Physics
Authors
U. Welp, G. Mu, R. Xie, A.E. Koshelev, W.K. Kwok, H.Q. Luo, Z.S. Wang, P. Cheng, L. Fang, C. Ren, H.-H. Wen,