Doping dependence of phase-separation morphology in (Sr,K)Fe2As2

Abstract

The effects of the possible phase separation on macroscopic transport properties are explored in (Sr,K)Fe 2 As 2 . Three probes, the low-field shielding 4πχ ZFC , the reversible diamagnetization M SC at 5 T, and the specific heat C p , with different characteristic length scales on the order of 10 3 , 10, and 10 0 nm, respectively, were used to examine several (Sr 1−x K x )Fe 2 As 2 samples. The data from different probes should be consistent if the sample can be regarded as mesoscopically homogeneous. While this seems to be the case for the optimally doped x = 0.45 samples, the apparent transition temperature and the effective superfluid density strongly depend on the probes used for both the underdoped (x = 0.3) and the overdoped (x = 0.7) samples. Discrepancies of up to a factor of 10 are observed. The data further suggest that both the x = 0.3 and x = 0.7 samples are better described as Josephson-junction arrays formed over separated superconductive domains of 10−10 2 nm sizes. Such a morphology evolution may drastically affect the interpretation of the observed doping effects.

Phase transition in CaFeAsH: bridging 1111 and 122 iron-based superconductors

“…(for LaFeAsO, there are three optical modes at 100, 180 and 290 cm-1) [53][54][55][56][57] The parameters extracted from this fit were γ = 8.18 (19) mJ/molK, ΘD = 324 (1) K, ΘE = 823 J/molK for LaFeAsO and SrFeAsF, respectively), 28,58 and smaller than those of conventional 122-and 11-type compounds (e.g., 1.0 and 3.2 J/molK for SrFe2As2 and FeTe, respectively). 25,59 In the normal relaxation method, the specific heat at each temperature is obtained by fitting the temperature-time relaxation curve.…”