Nodal Gap in Fe-Based Layered Superconductor LaO0.9F0.1-δFeAs Probed by Specific Heat Measurements

We report the specific heat measurements on the newly discovered Fe-based layered LaO0.9F 0.1-δFeAs superconductor with the onset transition temperature Tc≈28K. A nonlinear magnetic field dependence of the electronic specific heat coefficient γ(H) has been found in the low temperature limit, which is consistent with the prediction for a nodal superconductor. The maximum gap value ∆0≈3.4 ±0.5meV is derived by analysing γ(H) based on the d-wave model. We also detected the electronic specific heat difference between 9T and 0T in a wide temperature range, a specific heat anomaly can be clearly observed near Tc. The Debye temperature of our sample is determined to be about 315.7K. Our results suggest an unconventional mechanism for this new superconductor.