Interpretation of the in-plane infrared response of the high-Tc cuprate superconductors involving spin fluctuations revisited

TL;DR

This paper revisits the interpretation of the in-plane infrared response of high-Tc cuprate superconductors using a spin-fermion model, clarifying the physical origins of spectral features and analyzing temperature-dependent effects.

Contribution

It provides a detailed interpretation of infrared spectral features in high-Tc cuprates, emphasizing the role of spin fluctuations and offering insights into temperature effects on conductivity and kinetic energy.

Findings

Identified the physical meaning of spectral features related to the resonance mode.

Analyzed the influence of the spin-fluctuation continuum.

Explored temperature dependence of conductivity and kinetic energy.

Abstract

The in-plane infrared response of the high-Tc cuprate superconductors was studied using the spin-fermion model, where charged quasiparticles of the copper-oxygen planes are coupled to spin fluctuations. First, we analyzed structures of the superconducting-state conductivity reflecting the coupling of the quasiparticles to the resonance mode observed by neutron scattering. The conductivity computed with the input spin susceptibility in the simple form of the mode exhibits two prominent features: an onset of the real part of the conductivity starting around the frequency of the mode omega_{0} and a maximum of a related function W(omega), roughly proportional to the second derivative of the scattering rate, centered approximately at omega=omega_{0}+Delta_{0}/hbar, where Delta_{0} is the maximum value of the superconducting gap. The two structures are well known from earlier studies. Their physical meaning, however, has not been sufficiently elucidated thus far. Our analysis involving quasiparticle spectral functions provides a clear interpretation. Second, we explored the role played by the spin-fluctuation continuum. Third, we investigated the temperature dependence of the conductivity, of the intraband spectral weight, and of the effective kinetic energy. The changes of the latter two quantities below Tc are determined by the formation of the gap, by a feedback effect of the spin fluctuations on the quasiparticles, and by a significant shift of the chemical potential.