Unusual superconducting state at 49 K in electron-doped CaFe2As2 at ambient pressure

Proc Natl Acad Sci U S A. 2011 Sep 20;108(38):15705-9. doi: 10.1073/pnas.1112150108. Epub 2011 Sep 12.

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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Arsenicals / chemistry*
  • Atmospheric Pressure
  • Calcium Compounds / chemistry*
  • Crystallization
  • Electric Conductivity*
  • Electrons*
  • Ferrous Compounds / chemistry*
  • Phase Transition
  • Transition Temperature*
  • X-Ray Diffraction

Substances

  • Arsenicals
  • Calcium Compounds
  • Ferrous Compounds