Evidence for nodeless superconducting gap in NaFe1−xCoxAs from low-temperature thermal conductivity measurements
1 State Key Laboratory of Surface Physics, Department of Physics, and Laboratory of Advanced Materials, Fudan University - Shanghai 200433, PRC
2 Hefei National Laboratory for Physical Science at Microscale and Department of Physics, University of Science and Technology of China - Hefei, Anhui 230026, PRC
Received: 2 December 2012
Accepted: 20 December 2012
The thermal conductivity of optimally doped NaFe0.972Co0.028As (Tc ∼ 20 K) and overdoped NaFe0.925Co0.075As (Tc ∼ 11 K) single crystals were measured down to 50 mK. No residual linear term κ0/T is found in zero magnetic field for both compounds. Applying a field H = 3 T (≈Hc2/12) does not noticeably increase κ0/T in NaFe1.972Co0.028As. The κ0/T of overdoped NaFe1.925Co0.075As shows a field dependence similar to the optimally doped BaFe1.85Co0.15As2. All these results suggest nodeless superconducting gaps in NaFe1−xCoxAs from the optimal doping to the overdoped regime, with low anisotropy or ratio between the magnitudes of different gaps.
PACS: 74.70.Xa – Pnictides and chalcogenides / 74.25.fc – Electric and thermal conductivity
© EPLA, 2013