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, 1=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.
|Titolo:||Coexistence of two order parameters and a pseudogaplike feature in the iron-based superconductor LaFeAsO1−xFx|
|Data di pubblicazione:||2009|
|Digital Object Identifier (DOI):||10.1103/PhysRevB.79.184526|
|Appare nelle tipologie:||1.1 Articolo in rivista|