Exchange boson dynamics in cuprates: Optical conductivity of HgBa2CuO4+δ

The electron-boson spectral density function I2χ(Ω) responsible for carrier scattering of the high temperature superconductor HgBa2CuO4+δ (Tc=90K) is calculated from new data on the optical scattering rate. A maximum entropy technique is used. Published data on HgBa2Ca2Cu3O8+δ (Tc=130K) are also inverted and these new results are put in the context of other known cases. All spectra (with two notable exceptions) show a peak at an energy (Ωr) proportional to the superconducting transition temperature Ωr≈6.3kBTc. This charge channel relationship follows closely the magnetic resonance seen by polarized neutron scattering, Ωrneutron≈5. 4kBTc. The amplitudes of both peaks decrease strongly with increasing temperature. In some cases, the peak at Ωr is weak and the spectrum can have additional maxima and a background extending up to several hundred meV.