Coexistence of two order parameters and a pseudogaplike feature in the iron-based superconductor LaFeAsO_(1-x)F_x

Abstract

The nature and value of the order parameters (OPs) in the superconducting Fe-based oxypnictides REFeAsO_(1-x)F_x (RE = rare earth) are a matter of intense debate, also connected to the pairing mechanism which is probably unconventional. Point-contact Andreev-reflection experiments on LaFeAsO_(1-x)F_x gave us direct evidence of three energy scales in the superconducting state: a nodeless superconducting OP, Delta1 = 2.8-4.6 meV, which scales with the local Tc of the contact; a larger unconventional OP that gives conductance peaks at 9.8-12 meV, apparently closes below Tc and decreases on increasing the Tc of the contact; a pseudogaplike feature (i.e. a depression in the conductance around zero bias), that survives in the normal state up to T* ~ 140 K (close to the Neel temperature of the undoped compound), which we associate to antiferromagnetic spin fluctuations (AF SF) coexisting with superconductivity. These findings point toward a complex, unconventional nature of superconductivity in LaFeAsO_(1-x)F_x.

19 pages, 12 figures - one figure and some insets added, minor changes to the text

References in corpus (16)

• Magnetic Order versus superconductivity in the Iron-based layered La(O1-xFx)FeAs systems
• LaFeAsO${}_{1-x}$F${}_x$: A low carrier density superconductor near itinerant magnetism
• Observation of Fermi-surface-dependent nodeless superconducting gaps in Ba0.6K0.4Fe2As2
• Competing Orders and Spin-Density-Wave Instability in La(O${}_{1-x}$F${}_x$)FeAs
• Is LaO${}_{1-x}$F${}_x$FeAs an electron-phonon superconductor ?
• Very High Field Two-Band Superconductivity in LaFeAsO_0.89F_0.11
• The BCS-like gap in superconductor SmFeAsO_0.85F_0.15
• The role of critical current on point contact Andreev Reflection spectrum between a normal metal and a superconductor
• Evolution of the electronic excitation spectrum with strongly diminishing hole-density in superconducting Bi_{2}Sr_{2}CaCu_{2}O_{8+δ}
• Scanning tunneling spectroscopy of SmFeAsO0.85: Possible evidence for d-wave order parameter symmetry
• Nodal Superconductivity with Multiple Gaps in SmFeAsO${}_{0.9}$F${}_{0.1}$
• Possible two-gap superconductivity in NdFeAs(O,F) probed by point-contact Andreev-reflection spectroscopy
• Evidence for gap anisotropy in CaC6 from directional point-contact spectroscopy
• Neutron scattering study of the oxypnictide superconductor La(O,F)FeAs
• Point contact Andreev reflection spectroscopy of NdFeAsO_0.85
• Superconductivity at 41.0 K in the F-doped LaFeAsO1-xFx

Cited by in corpus (1)

• Thermal properties of SmFeAs(O1-xFx) as probe of the interplay between electrons and phonons