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TT: Fachverband Tiefe Temperaturen

TT 21: Superconductivity: Poster Session

TT 21.28: Poster

Montag, 16. März 2015, 15:00–18:00, Poster B

Superconducting properties and pseudogap from preformed Cooper pairs in the triclinic (CaFe_1−xPt_xAs)₁₀Pt₃As₈ — •M. A. Surmach¹, F. Brückner¹, S. Kamusella¹, R. Sarkar¹, P. Y. Portnichenko¹, J. T. Park², G. Ghambashidze³, H. Luetkens⁴, P. Biswas⁴, W. J. Choi⁵, Y. I. Seo⁵, Y. S. Kwon⁵, H.-H. Klauss¹, and D. S. Inosov¹ — ¹TU Dresden, Germany — ²MLZ, Garching, Germany — ³MPI, Stuttgart, Germany — ⁴PSI, Villigen, Switzerland — ⁵DGIST, Daegu, Republic of Korea

Using µSR, INS and NMR, we investigated the novel Fe-based superconductor with a triclinic crystal structure (CaFe_1−xPt_xAs)₁₀Pt₃As₈ (T_c=13 K). The T-dependence of the superfluid density from the µSR measurements indicates the presence of two superconducting gaps. Our INS data revealed commensurate spin fluctuations at the (π, 0) wave vector. Their intensity remains unchanged across T_c, indicating the absence of a spin resonance typical for many Fe-pnictides. Instead, we observed a peak around ω₀ = 7 meV at the same wave vector, which persists above T_c and is characterized by the ratio ω₀/k_BT_c≈6.2, i.e. significantly higher than typical values for the magnetic resonant modes in iron pnictides (∼ 4.3). The T-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=/T₁T, 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−xPt_xAs)₁₀Pt₃As₈, likely associated with the emergence of preformed Cooper pairs.