Evidence for a preformed Cooper pair model in the pseudogap spectra of a Ca10(Pt4As8)(Fe2As2)5 single crystal with a nodal superconducting gap

Abstract

For high- T c superconductors, clarifying the role and origin of the pseudogap is essential for understanding the pairing mechanism. Among the various models describing the pseudogap, the preformed Cooper pair model is a potential candidate. Therefore, we present experimental evidence for the preformed Cooper pair model by studying the pseudogap spectrum observed in the optical conductivity of a Ca 10 (Pt 4 As 8 )(Fe 2 As 2 ) 5 ( T c = 34.6 K) single crystal. We observed a clear pseudogap structure in the optical conductivity and observed its temperature dependence. In the superconducting (SC) state, one SC gap with a gap size of Δ = 26 cm −1 , a scattering rate of 1/τ = 360 cm −1 and a low-frequency extra Drude component were observed. Spectral weight analysis revealed that the SC gap and pseudogap are formed from the same Drude band. This means that the pseudogap is a gap structure observed as a result of a continuous temperature evolution of the SC gap observed below T c . This provides clear experimental evidence for the preformed Cooper pair model.

Unravelling the mechanism of the semiconducting-like behavior and its relation to superconductivity in (CaFe1−xPtxAs)10Pt3<

“…The similarity between the phase diagrams of Pt-doped Ca10-3-8, and Ca 10-3-8 under pressure, indicates the intrinsic nature of the semiconducting-like behavior. Moreover, the low-energy peak observed in Pt-doped Ca 10-3-8, has also been seen in La-doped Ca 8.5 La 1.5 (Pt 3 As 8 )(Fe 2 As 2 ) 5 (out-of-plan doping) [51], and in stoichiometric (CaFeAs) 10 Pt 4 As 8 [52]. The 2D nature of these materials will greatly increase the importance of spin fluctuations, suggesting that they may be playing a prominent role in the in-plane transport properties.…”

In-plane p-wave coherence length in iron-based superconductors

“…Both phases have been extensively studied [58][59][60][61]. As this showed in recent experiments by 10-4-8 phase demonstrates very unusual pairing behaviour [62]. In Fig.…”

Optical Properties in The Hole-Doped Ca8.5Na1.5(Pt3As8)(Fe2As2)5 Single Crystal

“…These results indicate that the two types of superconducting gaps obtained by fitting above are derived from the same broad Drude band obtained in the normal state, which may physically mean that an anisotropic superconducting gap with nodes was formed in the broad Drude band. However, the anisotropic superconducting gap with the node does not completely suppress the optical conductivity in the low frequency region and leaves a weak Drude response 35 . This is completely different from our results.…”