Symmetry of the superconducting gap in $HgB{a}_{2}CaC{u}_2{O}_{6+\hat{I}´}$ single crystals from electronic Raman scattering

Abstract

Pure electronic Raman spectra with no phonon structures superimposed to the electronic continuum, are reported for the first time, in optimally doped $HgB{a}_{2}CaC{u}_2{O}_{6+\hat{I}´}$ single crystals $(T_c=126$ K). Our low temperature spectra (15 K) for the $A_{1g}$, $B_{1g}$ and $B_{2g}$ symmetries exhibit striking differences with previous data in $B{i}_{2}S{r}_{2}CaC{u}_2{O}_{8+\hat{I}´}.$ The shape of the spectra for the various symmetries cannot be fitted by Devereaux's $d_{x^2-y^2}$ calculations, but strongly suggests a $d_{xy}$ gap, with its minima in the [100] and [010] directions.

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