Three-Dimensional Anisotropic Fluctuation Diamagnetism Around the Superconducting Transition of Ba1−x K x Fe2As2 Single Crystals in the Finite-Field (or Prange) Regime

Abstract

The magnetization around the superconducting transition was recently measured in a high-quality Ba 1-x K x Fe 2 As 2 single crystal with magnetic fields applied along and transverse to the crystal Felayers [J. Mosqueira et al., Phys. Rev. B 83, 094519 (2011)]. Here we extend this study to the finite field (or Prange) regime, in which the magnetic susceptibility is expected to be strongly dependent on the applied magnetic field. These measurements are analyzed in the framework of the threedimensional anisotropic Ginzburg Landau (3D-aGL) approach generalized to the short wavelength regime through the introduction of a total-energy cutoff in the fluctuation spectrum. The results further confirm the adequacy of GL approaches to describe the fluctuation effects close to the superconducting transition of these materials.

Non-conventional superconducting fluctuations in Ba(Fe1−xRhx)2As2 iron-based superconductors

“…The absence of the scaling suggests that a different fluctuating mechanism has to be found. We note that our data are not in disagreement with recent results on ironpnictides [34], since we are dealing with a weak field region. On the contrary at stronger fields, the 3D scaling is recovered, as also shown in figure 7.…”

Measurements of the superconducting fluctuations in optimally-doped BaFe$_{2-x}$Ni$_x$As$_2$ under high magnetic fields: Probing the 3D anisotropic Ginzburg-Landau approach

“…One of them is their dimensionality. In these materials the transverse coherence length amplitude ξ c (0) is close to the Fe layers periodicity length, s. Thus, depending on the particular compound studied, some works report a two-dimensional (2D) behavior [3,10,20] similar to the one found in highly anisotropic HTSC, [24] while others find three-dimensional (3D) characteristics, [4,5,6,7,11,12,14,15,16,19,21,22,23] or even a 3D-2D transition [8,13,18] when increasing the temperature above T c (as in optimally-doped YBa 2 Cu 3 O 7−δ ) [24]. ‡ But it was recently reported that the fluctuation electrical conductivity above T c of clean LiFeAs crystals seemingly follows a well defined 2D behavior (in both the amplitude and the reducedtemperature dependence), despite that for this compound ξ c (0) ≈ 1.6 nm is much larger than the Fe-layers periodicity length (s = 0.636 nm).…”

“…[3] In addition to their intrinsic interest, the superconducting fluctuation effects are a very useful tool to characterize the nature of a superconducting transition and to obtain material parameters, [2] so that different works have already addressed their study in FeSC through observables like the magnetization, specific heat or the electric conductivity. [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23] However, some fundamental aspects of the phenomenology of the fluctuation effects in these materials are still debated. One of them is their dimensionality.…”

Large increase of the anisotropy factor in the overdoped region of Ba(Fe$_{1-x}$Ni$_x$)$_2$As$_2$ as probed by fluctuation spectroscopy

“…The fluctuation effects have been recently used in a number of works to characterize the superconducting properties of Fe-based superconductors, through observables like the electrical conductivity, magnetization, or specific heat [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25]. Nowadays, the properties of these materials at the optimal doping were extensively studied and are already rather well understood.…”