Angular-dependent magnetic torque iniron-pnictide BaFe2−xNixAs2

摘要

Angular-dependent torque measurements have been performed on the electron dopediron-pnictide superconductors BaFe2−xNixAs2with series of Ni concentrations. In thesuperconducting state, an irreversibility, as the evidence for the presence of vortex, isobserved between the torque measured with increasing and decreasing angle. Our resultsin underdoped samplesx= 0.065 show that the irreversible torque signal survives up to atemperatureTirrwell above the superconducting transition temperatureTc, suggestingthe existence of superconducting vortices aboveTc, which is likely to originate fromsuperconducting fluctuations.