On the peak in the far-infrared conductivity of strongly anisotropic cuprates

TL;DR

This paper studies the far-infrared conductivity of electron-doped cuprates with a slight tilt, revealing a finite-frequency peak due to anisotropic mixing, and identifies a Josephson plasma resonance in the superconducting state.

Contribution

It provides new insights into the anisotropic conductivity response and extracts the c-axis conductivity, highlighting the Josephson plasma resonance in cuprates.

Findings

Finite-frequency peak at ~50 cm^{-1} due to anisotropic mixing.

Disappearance of the peak in pure in-plane response.

Identification of Josephson plasma resonance at 11.7 cm^{-1} in the superconducting state.

Abstract

We investigate the far-infrared and submillimeter-wave conductivity of electron-doped La_(2-x)Ce_xCuO_4 tilted 1 degree off from the ab-plane. The effective conductivity measured for this tilt angle reveals an intensive peak at finite frequency (\nu ~ 50 cm{-1}) due to a mixing of the in-plane and out-of-plane responses. The peak disappears for the pure in-plane response and transforms to the Drude-like contribution. Comparative analysis of the mixed and the in-plane contributions allows to extract the c-axis conductivity which shows a Josephson plasma resonance at 11.7 cm{-1} in the superconducting state.