The peculiar physical properties and phase diagram of BaFe_2-<i>x</i>Co_<i>x</i>As₂single crystals

Abstract

In this paper, we systematically study the transport, susceptibility and heat capacity of single crystals of BaFe2−xCoxAs2. In the underdoped region, spin density wave (SDW) transition was observed in both resistivity and susceptibility. The magnetic susceptibility shows unusual T-linear dependence above the SDW transition up to 700 K. With Co doping, SDW ordering is gradually suppressed and superconductivity emerges with a dome-like shape. The electrical transport, specific heat and magnetic susceptibility indicate that the SDW and superconductivity coexist in the BaFe2−xCoxAs2 sample around x=0.17, similar to the case of (Ba,K)Fe2As2. The superconductivity completely disappears for samples with x>0.34. A crossover from the SDW state to the Fermi-liquid state is observed with an increase in Co doping. A detailed electronic phase diagram of the evolution from the SDW to the superconducting state is given.