Fluctuation conductivity and possible pseudogap state in FeAs-based superconductor EuFeAsO_0.85F_0.15

Fluctuation induced conductivity and pseudogap state studies of Bi1.6Pb0.4Sr2Ca2Cu3O10+δ superconductor added with ZnO nanoparticles

“…The excess conductivity (Fluctuation induced conductivity) Δσ is defined as a difference between measured conductivity σ(T) and the normal state conductivity σ n (T) extrapolated to the low T region 69 . It can be calculated as: where ρ(T) is the measured resistivity and ρ n (T) is the normal state resistivity extrapolated to the low T region.…”

Fluctuating Cooper pairs in FeSe at temperatures exceeding double Tc

“…However, below ∼ 300 K, ρ(T ) transforms into roughly metallic-like dependence [3,12], and takes a shape resembling that observed for underdoped cuprate HTSCs (cuprates) [7,13] and FeAs-based superconductors (Fe-pnictides) [14,15]. Eventually, as T decreases, FeSe becomes superconducting (SC) with SC transition temperature T c ≈ 10 K at ambient pressure [1- 3,6,7], unexpectedly in a rather narrow range of Se concentration [16].…”

“…A significant part of the SC properties of HTSCs, both cuprates [77] and Fe-pnictides [5,15], is determined by the extremely short coherence length in these compounds, ξ, which determines the size of the Cooper pairs, both in the ab-plane, ξ ab , and along the c-axis, ξ c , which at low temperatures is smaller or comparable with the lattice parameter d along this axis ( [37,70], and references therein). We consider ξ(T ) = ξ(0)ε −1/2 , where ξ(0) is the coherence length at T = 0 and ε is a reduced temperature, as defined by Eq.…”

“…This is because above T 01 , which actually limits the range of SC fluctuations from above, ξ c (T ) is lower than the distance d 01 [11,36,77,80]. This, in turn, means that at T > T 01 > T 0 all charge carriers, including the FCPs, are believed to be mainly confined within conducting As-Fe-As layers (Fe-pnictides) [15] or CuO 2 planes (cuprates) [77], forming the quasi-2D conducting system [37,76,80,[82][83][84][85]. At those temperatures, because ξ c (T ) < d 01 , there is no direct interaction even between the internal conducting planes and now σ ′ (ε) does not obey any conventional fluctuation theory.…”

Diffusion of the superconducting transition in HTSC

“…This "diffusion" of the superconducting transition is due to the inhomogeneity of the material structure and to the presence of fluctuation Cooper pairs above T c . In this case, a certain influence could have the specific mechanisms of quasiparticle scattering [19][20][21][22][23], due to the presence in the system of kinetic and structural anisotropy.…”