Low energy excitations in superconducting ${\mathrm{La}}_{1.86}$${\mathrm{Sr}}_{0.14}$${\mathrm{CuO}}_4$

We present magnetic neutron scattering and specific heat data on the high-${\mathit{T}}_{\mathit{c}}$ superconductor ${\mathrm{La}}_{1.86}$ ${\mathrm{Sr}}_{0.14}$ ${\mathrm{CuO}}_4$. Both types of measurements show that even when the samples are superconducting, there are excitations with energies well below 3.5${\mathit{k}}_{\mathit{B}}$ ${\mathit{T}}_{\mathit{c}}$. These excitations coincide with a magnetic response, χ’ ’, whose amplitude is considerably below that observed at ${\mathit{T}}_{\mathit{c}}$=35±1 K. At the same time, the wave-vector dependence of χ’ ’ 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 of the type induced by localized magnetic impurities, clearly observed in the specific heat measurements.