Energy gap and Korringa constant in the high-temperature superconductor ${\mathrm{La}}_{1.83}$${\mathrm{Sr}}_{0.17}$Cu${\mathrm{O}}_4$ determined by NMR

Polycrystalline samples of ${\mathrm{La}}_{1.83}$${\mathrm{Sr}}_{0.17}$Cu${\mathrm{O}}_4$ were studied by pulsed nuclear-magnetic-resonance methods on the copper nucleus over a temperature range which included both normal and superconducting phases. A Korringa constant 14±1 K sec and a minimum value for the energy gap $\frac{2\Delta }{k_B{T}_c}=1.3\mathrm{}\pm 0.2$ were found. A comparison of these results with the larger gap reported from infrared absorption and from tunneling experiments indicates that there is substantial anisotropy in the pairing interaction. Homogeneous line narrowing in the superconducting state was observed.