Coexistence of two order parameters and a pseudogaplike feature in the iron-based superconductor LaFeAsO1−xFx

Abstract

The nature and value of the order parameters (OPs) in the superconducting Fe-based oxypnictides REFeAsO1−xFx (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 LaFeAsO1−xFx gave us direct evidence of three energy scales in the superconducting state: a nodeless superconducting OP, Δ1=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 Néel temperature of the undoped compound), which we associate to antiferromagnetic spin fluctuations coexisting with superconductivity. These findings point toward a complex, unconventional nature of superconductivity in LaFeAsO1−xFx.

Source-reported materials — not catalogue approval

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