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

Abstract

<p>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 hole-doped iron-based superconductor Ba1−xKxFe2As2. Compositions of the samples studied spanned from under- doped 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.</p>