Bosonic spectral density of epitaxial thin-film La1.83Sr0.17CuO4 superconductors from infrared conductivity measurements

TL;DR

This study uses optical spectroscopy and Eliashberg formalism to extract the bosonic spectral density in La1.83Sr0.17CuO4 thin films, revealing a two-component structure that correlates with spin excitations and explains differences in superconducting transition temperatures.

Contribution

It introduces a method to determine the bosonic spectral density in LSCO films and compares its temperature evolution with other cuprates, linking spectral features to superconducting properties.

Findings

Bosonic spectral density shows a two-peak structure matching spin excitation spectra.

Temperature evolution of spectral density differs from other cuprates.

Spectral functions explain the lower Tc of LSCO compared to Bi-2212.

Abstract

We use optical spectroscopy to investigate the excitations responsible for the structure in the optical self-energy of thin epitaxial films of La1.83Sr0.17CuO4. Using Eliashberg formalism to invert the optical spectra we extract the electron-boson spectral function and find that at low temperature it has a two component structure closely matching the spin excitation spectrum recently measured by magnetic neutron scattering. We contrast the temperature evolution of the spectral density and the two-peak behavior in La2-xSrxCuO4 with another high temperature superconductor Bi2Sr2CaCu2O8+d. The bosonic spectral functions of the two materials account for the low Tc of LSCO as compared to Bi-2212.