title: Unusual superconducting state at 49 K in electron-doped CaFe2As2 at ambient pressure.
abstract: We report the detection of unusual superconductivity up to 49 K in single crystalline CaFe(2)As(2) via electron-doping by partial replacement of Ca by rare-earth. The superconducting transition observed suggests the possible existence of two phases: one starting at 49 K, which has a low critical field < 4 Oe, and the other at 21 K, with a much higher critical field > 5 T. Our observations are in strong contrast to previous reports of doping or pressurizing layered compounds AeFe(2)As(2) (or Ae122), where Ae = Ca, Sr, or Ba. In Ae122, hole-doping has been previously observed to generate superconductivity with a transition temperature (T(c)) only up to 38 K and pressurization has been reported to produce superconductivity with a T(c) up to 30 K. The unusual 49 K phase detected will be discussed.
authors.affiliation: Texas Center for Superconductivity, University of Houston, Houston TX 77204-5002, USA.
authors.forename: Bing
authors.initials: B
authors.lastname: Lv
authors.forename: Liangzi
authors.initials: L
authors.lastname: Deng
authors.forename: Melissa
authors.initials: M
authors.lastname: Gooch
authors.forename: Fengyan
authors.initials: F
authors.lastname: Wei
authors.forename: Yanyi
authors.initials: Y
authors.lastname: Sun
authors.forename: James K
authors.initials: JK
authors.lastname: Meen
authors.forename: Yu-Yi
authors.initials: YY
authors.lastname: Xue
authors.forename: Bernd
authors.initials: B
authors.lastname: Lorenz
authors.forename: Ching-Wu
authors.initials: CW
authors.lastname: Chu
mesh_terms: D001152:Arsenicals / Q000737:chemistry*; D001274:Atmospheric Pressure; D017610:Calcium Compounds / Q000737:chemistry*; D003460:Crystallization; D004553:Electric Conductivity; D004583:Electrons; D005296:Ferrous Compounds / Q000737:chemistry*; D044367:Phase Transition; D044366:Transition Temperature; D014961:X-Ray Diffraction
chemical_list: D001152:Arsenicals; D017610:Calcium Compounds; D005296:Ferrous Compounds