Electronic Raman scattering in HgBa_{2}Ca_{2}Cu_{3}O_{8+δ} single crystals. Analysis of the superconducting state

Abstract

Electronic Raman scattering measurements have been performed on $HgB{a}_{2}C{a}_{2}C{u}_3{O}_{8+\hat{I}´}$ single crystals in the superconducting state. Pure electronic Raman spectra with no phonon structures hindering the analysis of the electronic continuum have been obtained. As a consequence, the spectra in the pure $B_{1g}$ and $B_{2g}$ symmetries are directly and reliably analyzed and the pure $A_{1g}$ contribution can be easily identified. Below the critical temperature $T_c,$ two electronic structures at $2\hat{I}”\sim 6.4k_B{T}_c$ and $2\hat{I}”\sim 9.4$ $k_B{T}_c$ are clearly seen. Both are observed simultaneously in pure $A_{1g}$ symmetry, the highest energy one being located at the energy of the $B_{1g}$ maximum. These two maxima disappear at $T_c$ and do not soften significantly as the temperature is raised up to $T_c.$ The low energy frequency dependence of the $B_{1g}$ electronic response is strongly linear, for various excitation lines in the 476.5 to 647.1 nm range. Such experimental data cannot be reconciled with a pure $d_{x^2-y^2}$ symmetry. Instead, they strongly advocate in favor of an anisotropic superconducting gap with two distinct gap maxima and of nodes existing outside the [110] and [1,$\bar{1}$,0] directions in {\bf k}-space. We discuss in detail the simplest order parameter compatible with our experimental findings.

12 pages, revtex, 12 figures