Upper and lower critical magnetic fields of superconducting NdFeAsO1−xFx single crystals studied by Hall-probe magnetization and specific heat

International audienceThe upper and lower critical fields have been deduced from specific heat and Hall-probe magnetization measurements in nonoptimally doped Nd O,F FeAs single crystals Tc 32-35 K . The anisotropy of the penetration depth is temperature independent and on the order of 4.0 1.5. Similarly specific-heat data lead to an anisotropy of the coherence length 5.5 1.5 close to Tc. Our results suggest the presence of rather large thermal fluctuations and the existence of a vortex liquid phase over a broad temperature range 5 K large at 2 T