Experimental Test of the Inter-Layer Pairing Models for High-Tc Superconductivity Using Grazing Incidence Infrared Reflectometry

TL;DR

This study measures the c-axis Josephson plasma frequencies in high-Tc cuprates using grazing incidence infrared reflectometry, testing models of inter-layer pairing mechanisms in superconductivity.

Contribution

It provides experimental data on plasma frequencies in specific cuprates, challenging recent theoretical predictions of inter-layer tunneling models.

Findings

Detected plasma resonance at 50 cm^{-1} in La_{2-x}Sr_xCuO_4

Established an upper limit of 100 cm^{-1} for Tl_2Ba_2CuO_6

Contradicts recent predictions of high plasma frequency from inter-layer tunneling models

Abstract

From measurements of the far-infrared reflectivity at grazing angles of incidence with p-polarized light we determined the c-axis Josephson plasma frequencies of the single layer high T_c cuprates Tl_2Ba_2CuO_6 and La_{2-x}Sr_xCuO_4. We detected a strong plasma resonance at 50 cm^{-1} for La_{2-x}Sr_xCuO_4 in excellent agreement with previously published results. For Tl_2Ba_2CuO_6 we were able to determine an upper limit of the unscreened c-axis Josephson plasma frequency 100 cm^{-1} or a c-axis penetration depth > 15 \mu m. The small value of $\omega_J$ stands in contrast to recent a prediction based on the inter-layer tunneling mechanism of superconductivity.