Superconducting properties and pseudogap from preformed Cooper pairs in the triclinic(CaFe1−xPtxAs)10Pt3

Abstract

Using a combination of muon-spin relaxation (μSR), 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 c = 13 K), containing platinum-arsenide intermediary layers. The temperature dependence of the superfluid density obtained from the μSR relaxation-rate measurements indicates the presence of two superconducting gaps, 1 2 . According to our INS measurements, commensurate spin fluctuations are centered at the (π, 0) wave vector, like in most other iron arsenides. Their intensity remains unchanged across T 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 ω 0 = 7 meV at the same wave vector, which persists above T c and is characterized by the ratio ω 0 /k B T c ≈ 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 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.

Doping evolution of spin fluctuations and their peculiar suppression at low temperatures in Ca(Fe1−xCox)2As2Sapkota1, Das2, Böhmer3 et al. 2018Phys. Rev. B72120View full textAdd to dashboardCite

“…Further, the spin-resonance peak occurs at the same values of E for T * > T > T c and T < T c , for both the cuprate [56] and iron-arsenide [55] superconductors, and, generally, the magnetic-scattering intensity at values of E lower than the resonance peak is suppressed. In contrast, we find a suppression of χ (Q stripe ,E) for Ca(Fe 0.97 Co 0.03 ) 2 As 2 at values of E much larger than the expected resonance energy of E res ≈ 5.4 meV, which differs with previous results for materials displaying a pseudogap [55,56]. However, as noted above, INS measurements specifically targeting lower values of E at positions corresponding to Q stripe are required to make a firm conclusion about the existence of a spin-resonance peak in Ca(Fe 0.97 Co 0.03 ) 2 As 2 .…”

“…For example, a spin-resonance peak is found for (CaFe 1−x Pt x As) 10 Pt 3 As 8 above T c [55]. Further, the spin-resonance peak occurs at the same values of E for T * > T > T c and T < T c , for both the cuprate [56] and iron-arsenide [55] superconductors, and, generally, the magnetic-scattering intensity at values of E lower than the resonance peak is suppressed.…”

“…For example, a spin-resonance peak is found for (CaFe 1−x Pt x As) 10 Pt 3 As 8 above T c [55]. Further, the spin-resonance peak occurs at the same values of E for T * > T > T c and T < T c , for both the cuprate [56] and iron-arsenide [55] superconductors, and, generally, the magnetic-scattering intensity at values of E lower than the resonance peak is suppressed. In contrast, we find a suppression of χ (Q stripe ,E) for Ca(Fe 0.97 Co 0.03 ) 2 As 2 at values of E much larger than the expected resonance energy of E res ≈ 5.4 meV, which differs with previous results for materials displaying a pseudogap [55,56].…”

Optical properties of optimally doped single-crystal Ca8.5La1.5(Pt3As8)(Seo1, Choi2, Kimura3 et al. 2017Phys. Rev. B116120View full textAdd to dashboardCite

“…More recently, Surmach et al 23 have performed a comprehensive measurements of muon-spin relaxation (µSR), inelastic neutron scattering (INS), and NMR on Pt-doped (CaFe 1−x Pt x As) 10 Pt 3 As 8 (T c = 13 K) -the same 10-3-8 compound we studied in this paper but with Pt doping on Fe sites. They found a PG behavior in the 1/T 1 data of 75 As NMR below T * ≈ 45 K (about three times higher than T c ).…”

Unconventional superconductivity

“…In a doped triclinic 10-3-8 (non-magnetic) IBS, Tc=13 K, Surmach et al [500] using INS find an increase in scattered magnetic intensity (at the spin excitation peak energy) below T*=45 K. Using NMR, and contrary to most IBS results, Surmach et al find a strong decrease in 1/T1T starting below a T* of 31 K. In the related 10-4-8 IBS, Tc=33 K, Kobayashi et al [501] and also Ikeuchi et al [502] see no evidence of pseudogap behavior in their NMR data.…”