Doping evolution of the anisotropic upper critical fields in the iron-based superconductor Ba1−xKxFe2As2

In-plane resistivity measurements as a function of temperature and magnetic field up to 35 T with precise orientation within the crystallographic ac plane were used to study the upper critical field Hc2 of the holedoped iron-based superconductor Ba1−xKxFe2As2. Compositions of the samples studied spanned from underdoped x=0.17 (Tc=12 K) and x=0.22 (Tc=20 K), both in the coexistence range of stripe magnetism and superconductivity, through optimal doping x=0.39 (Tc=38.4 K) and x=0.47 (Tc=37.2 K), to overdoped x=0.65 (Tc=22 K) and x=0.83 (Tc=10 K). We find notable doping asymmetry of the shapes of the anisotropic Hc2(T), suggesting the important role of paramagnetic limiting effects in the H∥a configuration in overdoped compositions and multiband effects in underdoped compositions. Disciplines Condensed Matter Physics | Materials Science and Engineering Authors Makariy A. Tanatar; Yong Liu; J. Jaroszynski,; J. S. Brooks; Thomas A. Lograsso; and Ruslan Prozorov PHYSICAL REVIEW B 96, 184511 (2017) Doping evolution of the anisotropic upper critical fields in the iron-based superconductor Ba1−xKxFe2As2 M. A. Tanatar,1,2 Yong Liu,1 J. Jaroszynski,3 J. S. Brooks,3,* T. A. Lograsso,1,4 and R. Prozorov1,2 1Ames Laboratory, U.S. DOE, Ames, Iowa 50011, USA 2Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA 3National High Magnetic Field Laboratory, Florida State University, Tallahassee, Florida 32310, USA 4Department of Materials Science and Engineering, Iowa State University, Ames, Iowa 50011, USA (Received 21 August 2017; revised manuscript received 19 October 2017; published 14 November 2017) In-plane resistivity measurements as a function of temperature and magnetic field up to 35 T with precise orientation within the crystallographic ac plane were used to study the upper critical field Hc2 of the holedoped iron-based superconductor Ba1−xKxFe2As2. Compositions of the samples studied spanned from underdoped x = 0.17 (Tc = 12 K) and x = 0.22 (Tc = 20 K), both in the coexistence range of stripe magnetism and superconductivity, through optimal doping x = 0.39 (Tc = 38.4 K) and x = 0.47 (Tc = 37.2 K), to overdoped x = 0.65 (Tc = 22 K) and x = 0.83 (Tc = 10 K). We find notable doping asymmetry of the shapes of the anisotropic Hc2(T ), suggesting the important role of paramagnetic limiting effects in the H ‖ a configuration in overdoped compositions and multiband effects in underdoped compositions. DOI: 10.1103/PhysRevB.96.184511