title: Energy gap evolution across the superconductivity dome in single crystals of (Ba1-xKx)Fe2As2.
abstract: The mechanism of unconventional superconductivity in iron-based superconductors (IBSs) is one of the most intriguing questions in current materials research. Among non-oxide IBSs, (Ba1-xKx)Fe2As2has been intensively studied because of its high superconducting transition temperature and fascinating evolution of the superconducting gap structure from being fully isotropic at optimal doping (x≈ 0.4) to becoming nodal atx> 0.8. Although this marked evolution was identified in several independent experiments, there are no details of the gap evolution to date because of the lack of high-quality single crystals covering the entire K-doping range of the superconducting dome. We conducted a systematic study of the London penetration depth, λ(T), across the full phase diagram for different concentrations of point-like defects introduced by 2.5-MeV electron irradiation. Fitting the low-temperature variation with the power law, Δλ ~Tn, we find that the exponentnis the highest and theTcsuppression rate with disorder is the smallest at optimal doping, and they evolve with doping being away from optimal, which is consistent with increasing gap anisotropy, including an abrupt change aroundx≃ 0.8, indicating the onset of nodal behavior. Our analysis using a self-consistentt-matrix approach suggests the ubiquitous and robust nature ofs±pairing in IBSs and argues against a previously suggested transition to ad-wave state nearx= 1 in this system.
authors.affiliation: Ames Laboratory, Ames, IA 50011, USA.; Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA.
authors.forename: Kyuil
authors.initials: K
authors.lastname: Cho
authors.affiliation: Laboratoire des Solides Irradiés, École Polytechnique, CNRS, CEA, Université Paris-Saclay, 91128 Palaiseau Cedex, France.
authors.forename: Marcin
authors.initials: M
authors.lastname: Kończykowski
authors.affiliation: Ames Laboratory, Ames, IA 50011, USA.; Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA.
authors.forename: Serafim
authors.initials: S
authors.lastname: Teknowijoyo
authors.affiliation: Ames Laboratory, Ames, IA 50011, USA.; Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA.
authors.forename: Makariy A
authors.identifier: 0000-0003-2129-9833
authors.initials: MA
authors.lastname: Tanatar
authors.affiliation: Ames Laboratory, Ames, IA 50011, USA.
authors.forename: Yong
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Ames Laboratory, Ames, IA 50011, USA.; Department of Materials Science and Engineering, Iowa State University, Ames, IA 50011, USA.
authors.forename: Thomas A
authors.identifier: 0000-0002-8441-5320
authors.initials: TA
authors.lastname: Lograsso
authors.affiliation: Ames Laboratory, Ames, IA 50011, USA.
authors.forename: Warren E
authors.identifier: 0000-0003-3994-7624
authors.initials: WE
authors.lastname: Straszheim
authors.affiliation: Joint Institute for Computational Sciences, University of Tennessee, Knoxville, TN 37996, USA.; Center for Nanophase Materials Sciences, Oak Ridge National Laboratory, Oak Ridge, TN 37831, USA.
authors.forename: Vivek
authors.initials: V
authors.lastname: Mishra
authors.affiliation: Department of Physics, University of Florida, Gainesville, FL 32611, USA.
authors.forename: Saurabh
authors.initials: S
authors.lastname: Maiti
authors.affiliation: Department of Physics, University of Florida, Gainesville, FL 32611, USA.
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Hirschfeld
authors.affiliation: Ames Laboratory, Ames, IA 50011, USA.; Department of Physics and Astronomy, Iowa State University, Ames, IA 50011, USA.
authors.forename: Ruslan
authors.identifier: 0000-0002-8088-6096
authors.initials: R
authors.lastname: Prozorov
mesh_terms: D016880:Anisotropy; D006358:Hot Temperature; D058085:Iron Compounds / Q000737:chemistry*; D008280:Magnetics / Q000379:methods; D060739:Phonons; D055585:Physical Phenomena; D000072176:Superconductivity
chemical_list: D058085:Iron Compounds
keywords: Superconductor; pairing symmetry; pnictides