Electronic Raman scattering in HgBa2Ca2Cu3O8+δ single crystals: Analysis of the superconducting state

Abstract

Electronic Raman-scattering measurements have been performed on HgBa2Ca2Cu3O8+δ 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 B1g and B2g symmetries are directly and reliably analyzed and the pure A1g contribution can be easily identified. Below the critical temperature Tc, two electronic structures at 2Δ∼6.4kBTc and 2Δ∼9.4kBTc are clearly seen. Both are observed simultaneously in pure A1g symmetry, the highest energy one being located at the energy of the B1g maximum. These two maxima disappear at Tc and do not soften significantly as the temperature is raised up to Tc. The low-energy frequency dependence of the B1g electronic response is strongly linear, for various excitation lines in the 476.5–647.1 nm range. Such experimental data cannot be reconciled with a pure dx2−y2 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 [1,1¯,0] directions in k space. We discuss in detail the simplest order parameter compatible with our experimental findings.

Source-reported materials — not catalogue approval

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