Multiple Andreev reflections spectroscopy of two-gap 1111- and 11 Fe-based superconductors

Abstract

Using the "break-junction" technique we prepared and studied superconductor - constriction - superconductor nanocontacts in polycrystalline samples of Fe-based superconductors CeO${}_{0.88}$F${}_{0.12}$FeAs (Ce-1111; $T_C^{\mathrm{bulk}}=41\pm 1K$), LaO${}_{0.9}$F${}_{0.1}$FeAs (La-1111; $T_C^{\mathrm{bulk}}=28\pm 1K$), and FeSe ($T_C^{\mathrm{bulk}}=12\pm 1K$). We detected two subharmonic gap structures related with multiple Andreev reflections, indicating the presence of two superconducting gaps with the BCS-ratios $2{\Delta }_L/k_B{T}_C=4.2÷5.9$ and $2{\Delta }_S/k_B{T}_C\sim 1\ll 3.52$, respectively. Temperature dependences of the two gaps ${\Delta }_{L,S}(T)$ in FeSe indicate a $k$-space proximity effect between two superconducting condensates. For the studied iron-based superconductors we found a linear relation between the gap ${\Delta }_L$ and magnetic resonance energy, $E_{\mathrm{res}}\approx 2{\Delta }_L$.

6 pages, 7 figures. Proceedings of FPS'11 conference

References in corpus (3)

• Strong-coupling Spin-singlet Superconductivity with Multiple Full Gaps in Hole-doped Ba${}_{0.6}$K${}_{0.4}$Fe${}_2$As${}_2$ Probed by Fe-NMR
• Inelastic neutron scattering study on the resonance mode in an optimally doped superconductor LaFeAsO${}_{0.92}$F${}_{0.08}$
• Temperature Dependence of Superconducting Gaps in Mg(Al)B2 System Investigated by SnS-Andreev Spectroscopy

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• Evolution of Superconducting Gaps in Th-Substituted Sm${}_{1-x}$Th${}_x$OFeAs Studied by Multiple Andreev Reflection Spectroscopy
• Spin-density-wave-induced anomalies in the optical conductivity of AFe2As2, (A=Ca, Sr, Ba) single-crystalline iron pnictides
• Spin resonance peak in Fe-based superconductors with unequal gaps
• Effect of gap anisotropy on the spin resonance peak in the superconducting state of iron-based materials
• Vortex Structure and Anisotropic Superconducting Gaps in Ba[Fe(Ni)]${}_2$As${}_2$
• Estimation of intraband and interband relative coupling constants from temperature dependences of the order parameter for two-gap superconductors
• Intrinsic charge dynamics in high-Tc AFeAs(O,F) superconductors
• Multiple energy gap features of superconducting FeSe investigated by tunneling spectroscopy
• Direct Evidence of Two Superconducting Gaps in FeSe${}_{0.5}$Te${}_{0.5}$: SnS-Andreev Spectroscopy and Lower Critical Field
• Intrinsic Multiple Andreev Reflections in layered Th-doped Sm${}_{1-x}$Th${}_x$OFeAs