Low energy excitations in superconducting La1.86Sr0.14CuO4.

Abstract

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, \ensuremath{\chi}'', whose amplitude is considerably below that observed at ${\mathit{T}}_{\mathit{c}}$=35\ifmmode\pm\else\textpm\fi{}1 K. At the same time, the wave-vector dependence of \ensuremath{\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 of the type induced by localized magnetic impurities, clearly observed in the specific heat measurements.