Giant anisotropy in superconducting single crystals of CsCa2Fe4As4F2

Abstract

We report the transport and magnetic measurements on single crystals of CsCa2Fe4As4F2, a recently discovered double-FeAs-layer superconductor with Tc∼30 K. We observed a large resistivity anisotropy of ρc(T)/ρab(T)∼103 that tends to increase with decreasing temperature. The ρc(T) data exhibit a nonmetallic behavior at high temperatures, suggesting an incoherent electronic state due to the dimension crossover. The superconducting onset transition temperature in ρab(T) is 0.7 K higher than that in ρc(T), reflecting two-dimensional (2D) superconducting fluctuations. The lower and upper critical fields also show an exceptionally high anisotropy among iron-based superconductors. The Hc1⊥(T) data are well fitted with two s-wave-like superconducting gaps, Δ1(0)=6.75 meV and Δ2(0)=2.32 meV. The interplane coherence length ξc(0) is estimated to be 3.6 Å, which is remarkably smaller than the distance between conducting layers (8.6 Å), consolidating the 2D nature in the title material.

Source-reported materials — not catalogue approval

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