Superconducting properties and pseudogap from preformed Cooper pairs in the triclinic (CaFe${}_{1-x}$Pt${}_x$As)${}_{10}$Pt${}_3$As${}_8$

Abstract

Using a combination of muon-spin relaxation ($\mu$SR), inelastic neutron scattering (INS) and nuclear magnetic resonance (NMR), we investigated the novel iron-based superconductor with a triclinic crystal structure (CaFe${}_{1-x}$Pt${}_x$As)${}_{10}$Pt${}_3$As${}_8$ (T${}_{\mathrm{c}}$ = 13 K), containing platinum-arsenide intermediary layers. The temperature dependence of the superfluid density obtained from the $\mu$SR relaxation-rate measurements indicates the presence of two superconducting gaps, ${\Delta }_{\text{1}}\gg {\Delta }_{\text{2}}$. According to our INS measurements, commensurate spin fluctuations are centered at the ($\pi$, 0) wave vector, like in most other iron arsenides. Their intensity remains unchanged across T${}_{\text{c}}$, indicating the absence of a spin resonance typical for many Fe-based superconductors. Instead, we observed a peak in the spin-excitation spectrum around $\hslash {\omega }_0=$7 meV at the same wave vector, which persists above T${}_{\mathrm{c}}$ and is characterized by the ratio $\hslash {\omega }_0/k_{\text{B}}{T}_{\text{c}}\approx$6.2, which is significantly higher than typical values for the magnetic resonant modes in iron pnictides (~4.3). The temperature dependence of magnetic intensity at 7 meV revealed an anomaly around T* = 45 K related to the disappearance of this new mode. A suppression of the spin-lattice relaxation rate, $1/T_{1}T$, observed by NMR immediately below T* without any notable subsequent anomaly at T${}_{\mathrm{c}}$, indicates that T* could mark the onset of a pseudogap in (CaFe${}_{1-x}$Pt${}_x$As)${}_{10}$Pt${}_3$As${}_8$, which is likely associated with the emergence of preformed Cooper pairs.

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Cited by in corpus (2)

• Unconventional Superconductivity
• Optical properties of the optimally doped Ca${}_{8.5}$La${}_{1.5}$(Pt${}_3$As${}_8$)(Fe${}_2$As${}_2$)${}_5$ single crystal