Large Anisotropic Uniaxial Pressure Dependencies ofTcin Single CrystallineBa(Fe0.92Co0.08)

Abstract

Using high-resolution dilatometry, we study the thermodynamic response of the lattice parameters to superconducting order in a self-flux grown Ba(Fe 0.92 Co 0.08 ) 2 As 2 single crystal. The uniaxial pressure dependencies of the critical temperature of T c , calculated using our thermal expansion and specific heat data via the Ehrenfest relation, are found to be quite large and very anisotropic (dT c /dp a = 3.1(1) K/GPa and dT c /dp c = -7.0(2) K/GPa). Our results show that there is a strong coupling of the c/a ratio to superconducting order, which demonstrates that T c is far from the optimal value. A surprising similarity with the uniaxial pressure effects in several other layered superconductors is discussed. 74.25.Bt, 74.62.Fj The recent discovery of superconductivity up to 26 K in a layered FeAs compound [1] has initiated a large research effort in these materials [2]. At the time of writing, the maximum values of the critical temperature, T c , of around 55 K [3,4] have been found in the ReOFeAs (Re -rare earth) or "1111" structural family. Superconductivity also occurs in a simpler class of materials based on the BaFe 2 As 2 parent compound ("122" structure) with T c values up to 38 K for K-doped 122 [5]. The 122 materials are particularly interesting for experimental studies, because fairly large flux-grown single crystals can readily be obtained [6,7]. Besides

Strange Inter-Layer Properties of Ba(Fe1-xCox)2As2 Appearing in Ultrasonic Measurements

“…Here, the uniaxial strain dependence d T sc /d ε i is related to the uniaxial pressure dependence of T sc as [26] from the thermal expansion measurement. We used C 11 , C 33 , and C 12 values of 109.2, 78.7, and 43.46 GPa, respectively, for the calculation.…”

Spin-density-wave-induced anomalies in the optical conductivity ofAFe2As2, (Charnukha1, Pröpper2, Larkin3 et al. 2013Phys. Rev. B2717531View full textAdd to dashboardCite

“…2,3 This fact owes to the early discovery 4,5 and synthesis of large high-quality single-crystalline compounds of this class, [6][7][8][9] thus allowing the entire arsenal of experimental condensed-matter techniques to be applied to them virtually simultaneously, giving rise to explosive progress in this area of research. The most attention of the community has since been focused on one particular member of the 122 class, BaFe 2 As 2 .…”

Lack of coupling between superconductivity and orthorhombic distortion in stoichiometric single-crystalline FeSe

“…With its huge sensitivity of T c to external pressure and the large separation between structurally distorted and magnetically ordered phase, FeSe is an intriguing system to study the phase interplay using pressure as a tuning parameter. Uniaxial pressure effects, as can be studied by thermal expansion, are of special interest, because they are usually very anisotropic in the iron-based systems due to the layered crystal structures [11,12]. Further, these types of measurements provide a sensitive probe of the coupling between superconducting and orthorhombic order parameters [13,14].…”

“…However, in Co-Ba122, in-plane and c-axis pressure derivatives have opposite signs and largely cancel in the hydrostatic average (with the negative p c derivative slightly prevailing) [11,13], while the p c derivative is approximately zero in FeSe. The structural tuning parameter of the 122-systems is the c/a ratio [12][13][14]. In FeSe instead, the in-plane distance alone appears to be the tuning parameter, which couples strongly to hydrostatic pressure.…”