Direct Observation of a Magnetic Gap in SuperconductingLa1.85Sr0.15CuO4(Tc=37.3K)

Abstract

Neutron inelastic scattering experiments have been performed on homogeneous single crystals of ${\mathrm{La}}_{1.85}{\mathrm{Sr}}_{0.15}{\mathrm{CuO}}_4$ with $T_c=37.3\mathrm{}$ K (at onset), higher than any previously studied single crystals. The temperature dependence of the low energy incommensurate peak intensity at $\left(\pi \right(1\pm \delta ),\pi )$ and $(\pi ,\pi (1\pm \delta \left)\right)$ exhibits a pronounced maximum near $T_c$. In contrast to the results reported on lower $T_c$ crystals, the intensity below 3.5 meV dramatically decreases as the temperature decreases below $T_c$, vanishing into the background below $\sim 15$ K. The behavior is consistent with predictions based on a $d_{x^2{-y}^2}$ superconducting order parameter.