Far-infrared and submillimeter-wave conductivity in electron-doped cuprate La_{2-x}Ce_xCuO_4

TL;DR

This study investigates the far-infrared and submillimeter-wave conductivity in electron-doped La_{2-x}Ce_xCuO_4, revealing d-wave superconductivity characteristics and similarities to hole-doped cuprates.

Contribution

It provides experimental evidence of d-wave symmetry and identifies specific conductivity features associated with superconducting gaps in electron-doped cuprates.

Findings

Gradual absorption onset inconsistent with s-wave gap

Observation of zero-frequency and finite-frequency peaks indicating d-wave symmetry

Infrared peak related to superconducting gap or spin-fluctuations

Abstract

We performed far-infrared and submillimeter-wave conductivity experiments in the electron-doped cuprate La_{2-x}Ce_xCuO_4 with x = 0.081 (underdoped regime, T_c = 25 K). The onset of the absorption in the superconducting state is gradual in frequency and is inconsistent with the isotropic s-wave gap. Instead, a narrow quasiparticle peak is observed at zero frequency and a second peak at finite frequencies, clear fingerprints of the conductivity in a d-wave superconductor. A far-infrared conductivity peak can be attributed to 4Delta_0, or to 2Delta_0 + Delta_spin, where Delta_spin is the resonance frequency of the spin-fluctuations. The infrared conductivity as well as the suppression of the quasiparticle scattering rate below T_c are qualitatively similar to the results in the hole-doped cuprates.