The electric quadrupole hyperfine interaction at Cu (100) surfaces has been detected at isolated ${}_{}{}^{111}{}_{}{}^{}\mathrm{In}$ probe atoms by use of the perturbed $\gamma \gamma$ angular correlation technique. The electric-field-gradient tensor at $T=295\mathrm{}$ K was found to be axially symmetric with a strength of $\left|V_{\mathrm{zz}}\mathrm{}\right|=1.0\left(2\mathrm{}\right)\mathrm{}\times {10}^{18}$ V/${\mathrm{cm}}^2$ and the symmetry axis perpendicular to the (100) surface. A linear temperature dependence of the electric field gradient was observed. These findings support the assumption of highly symmetric surface sites as positions for the ${}_{}{}^{111}{}_{}{}^{}\mathrm{In}$ probes.

• Received 26 June 1986

DOI:https://doi.org/10.1103/PhysRevLett.57.1068