Low energy excitations in superconducting La_1.86Sr_0.14CuO₄

We present magnetic neutron scattering and specific heat data on the high-T(c) superconductor La1.86Sr0.14CuO4. Even when the samples are superconducting and the magnetic response, chi'', is suppressed, there are excitations with energies well below 3.5k(B)T(c). The wave-vector dependence of chi'' is identical to that for the normal state, which implies that the low frequency excitations in our crystals are not those associated with the nodes of a clean d-wave superconductor.

However, the data are consistent with gapless superconductivity induced by localized magnetic impurities, clearly observed in the specific heat measurements.