Superconductivity of Co-Doped CaKFe4As4 Investigated via Point-Contact Spectroscopy and London Penetration Depth Measurements

Abstract

The iron-based superconductors (IBSs) of the recently discovered 1144 class, unlike many other IBSs, display superconductivity in their stoichiometric form and are intrinsically hole doped. The effects of chemical substitutions with electron donors are thus particularly interesting to investigate. Here, we study the effect of Co substitution in the Fe site of CaKFe${}_4$As${}_4$ single crystals on the critical temperature, on the energy gaps, and on the superfluid density by using transport, point-contact Andreev-reflection spectroscopy (PCARS), and London penetration depth measurements. The pristine compound (T${}_{\mathrm{c}}\simeq$ 36 K) shows two isotropic gaps whose amplitudes (${\Delta }_1$ = 1.4$-$3.9 meV and ${\Delta }_2$ = 5.2$-$8.5 meV) are perfectly compatible with those reported in the literature. Upon Co doping (up to $\approx$7% Co), T${}_{\mathrm{c}}$ decreases down to $\simeq$ 20 K, the spin-vortex-crystal order appears, and the low-temperature superfluid density is gradually suppressed. PCARS and London penetration depth measurements perfectly agree in demonstrating that the nodeless multigap structure is robust upon Co doping, while the gap amplitudes decrease as a function of T${}_{\mathrm{c}}$ in a linear way with almost constant values of the gap ratios 2${\Delta }_i$/k${}_{\mathrm{B}}$T${}_{\mathrm{c}}$.

11 pages, 4 figures

References in corpus (22)

• High-temperature superconductivity in iron-based materials
• Scale-free structural organization of oxygen interstitials in La2CuO4+y
• The role of critical current on point contact Andreev Reflection spectrum between a normal metal and a superconductor
• Superconductivity in KCa${}_2$Fe${}_4$As${}_4$F${}_2$ with Separate Double Fe${}_2$As${}_2$ Layers
• Crossover from weak to strong pairing in unconventional superconductors
• Competing orders in FeAs layers
• Specific heat evidence for two-gap superconductivity in ternary-iron silicide Lu${}_2$Fe${}_3$Si${}_5$
• Large and significantly anisotropic critical current density induced by planar defects in CaKFe4As4 single crystals
• Magnetic fluctuations and superconducting properties of CaKFe4As4 studied by 75As NMR
• Single-crystal growth and extremely high H_c2 of 12442-type Fe-based superconductor KCa_2Fe_4As_4F_2
• Comprehensive Eliashberg analysis of microwave conductivity and penetration depth of K-, Co-, and P-substituted BaFe2As2
• Electronic properties, low-energy Hamiltonian and superconducting instabilities in CaKFe${}_4$As${}_4$
• RbEu(Fe${}_{1-x}$Ni${}_x$)${}_4$As${}_4$: From a ferromagnetic superconductor to a superconducting ferromagnet
• Spin Resonance in the New-Structure-Type Iron-Based Superconductor CaKFe4As4
• Nodal multigap superconductivity in the anisotropic iron-based compound RbCa2Fe4As4F2
• Electrodynamic response of Ba(Fe1-xRhx)2As2 across the s+- to s++ order parameter transition
• Effects of isoelectronic Ru substitution at the Fe site on the energy gaps of optimally F-doped SmFeAsO
• Anisotropy induced vortex lattice rearrangement in CaKFe${}_4$As${}_4$
• Superconductivity of underdoped PrFeAs(O,F) investigated via point-contact spectroscopy and nuclear magnetic resonance
• Spectroscopic studies of the superconducting gap in the 12442 family of iron-based compounds
• A model for critical current effects in point-contact Andreev-reflection spectroscopy
• Unusually weak irradiation effects in anisotropic iron-based superconductor RbCa2Fe4As4F2

Cited by in corpus (1)

• Direct evidence for two-gap superconductivity in hydrogen-intercalated titanium diselenide