Lower critical field and SNS-Andreev spectroscopy of 122-arsenides: Evidence of nodeless superconducting gap

Abstract

Using two experimental techniques, we studied single crystals of the 122-FeAs family with almost the same critical temperature, Tc. We investigated the temperature dependence of the lower critical field of a single crystal under static magnetic fields parallel to the axis. The temperature dependence of the London penetration depth can be described equally well either by a single anisotropic -wave-like gap or by a two-gap model, while a d-wave approach cannot be used to fit the London penetration depth data. Intrinsic multiple Andreev reflection effect spectroscopy was used to detect bulk gap values in single crystals of the intimate compound, with the same Tc. We estimated the range of the large gap value 6-8 meV (depending on small variation of and its a space anisotropy of about 30%, and the small gap 1.7 meV. This clearly indicates that the gap structure of our investigated systems more likely corresponds to a nodeless s-wave two gaps.

9 pages, 6 figures

References in corpus (24)

• High-temperature superconductivity in iron-based materials
• Electronic Structure and Doping in BaFe${}_2$As${}_2$ and LiFeAs: Density Functional Calculations
• Microwave Penetration Depth and Quasiparticle Conductivity in PrFeAsO_1-y Single Crystals : Evidence for a Full-Gap Superconductor
• Iron based superconductors: magnetism, superconductivity and electronic structure
• Anisotropic Energy Gaps of Iron-based Superconductivity from Intra-band Quasiparticle Interference in LiFeAs
• Field and Temperature Dependence of the Superfluid Density in LaO_{1-x}F_xFeAs Superconductors: A Muon Spin Relaxation Study
• Unconventional London penetration depth in Ba(Fe0.93Co0.07)2As2 single crystals
• Upper critical field, anisotropy, and superconducting properties of Ba${}_{1-x}$K${}_x$Fe${}_2$As${}_2$ single crystals
• AFe2As2 (A = Ca, Sr, Ba, Eu) and SrFe_(2-x)TM_(x)As2 (TM = Mn, Co, Ni): crystal structure, charge doping, magnetism and superconductivity
• Observation of Lattice and Andreev Bound States of Vortices in Ba0.6K0.4Fe2As2 Single Crystals with Scanning Tunneling Microscopy/Spectroscopy
• Growth and characterization of A_{1-x}K_xFe_2As_2 (A = Ba, Sr) single crystals with x=0 - 0.4
• Coexistence of magnetic fluctuations and superconductivity in the pnictide high temperature superconductor SmFeAsO${}_{1-x}$F${}_x$ measured by muon spin rotation
• Evidence for Two Gaps and Breakdown of the Uemura Plot in Ba${}_{0.6}$K${}_{0.4}$Fe${}_2$As${}_2$ Single Crystals
• Temperature dependence of lower critical field Hc1(T) shows nodeless superconductivity in FeSe
• Lower Critical Fields of Superconducting PrFeAsO${}_{1-y}$ Single Crystals
• Existence, character and origin of surface-related bands in the high temperature iron pnictide superconductor BaFe_{2-x}Co_{x}As_{2}
• Upper and lower critical fields in NdFeAs(O,F) single crystals : a study by Hall probe magnetization and specific heat
• Anisotropic but nodeless superconducting gap in the presence of spin density wave in iron-pnictide superconductor NaFe1-xCoxAs
• Small anisotropy of the lower critical field and $s_{\pm }$-wave two-gap feature in single crystal LiFeAs
• Electronic band structure and momentum dependence of the superconducting gap in (Ca, Na)Fe2As2 from angle-resolved photoemission spectroscopy
• Lower Critical Field, Anisotropy, and Two-Gap Features of LiFeAs
• Specific Heat To Hc2: Evidence for Nodes or Deep Minima in the Superconducting Gap of Under- and Overdoped Ba(Fe1-xCox)2As2
• Unconventional superconductivity of NdFeAsO0.82F0.18 indicated by the low temperature dependence of the lower critical field Hc1
• ARPES observation of isotropic superconducting gaps in isovalent Ru-substituted Ba(Fe${}_{0.75}$Ru${}_{0.25}$)${}_2$As${}_2$

Cited by in corpus (12)

• Superconducting properties of sulfur-doped iron selenide
• Break-junction technique in application to layered superconductors (Review article)
• Nodeless superconductivity in the presence of spin-density wave in pnictide superconductors: The case of BaFe${}_{2-x}$Ni${}_x$As${}_2$
• Signature of multigap nodeless superconductivity in fluorine-doped NdFeAsO
• High-pressure behavior of superconducting boron-doped diamond
• Electronic Band Structure and Superconducting Properties of SnAs
• Type-II Superconductivity below 4K in Sn0.4Sb0.6
• On the Structure of Superconducting Order Parameter in High-Temperature Fe-Based Superconductors
• Spin resonance peak in Fe-based superconductors with unequal gaps
• Vortex Structure and Anisotropic Superconducting Gaps in Ba[Fe(Ni)]${}_2$As${}_2$
• Strong pinning in the hole-doped pnictide superconductor La${}_{0.34}$Na${}_{0.66}$Fe${}_2$As${}_2$
• Direct Evidence of Two Superconducting Gaps in FeSe${}_{0.5}$Te${}_{0.5}$: SnS-Andreev Spectroscopy and Lower Critical Field