Charge transfer gap for T'-RE2CuO4 and T-La2CuO4 as estimated from Madelung potential calculations

TL;DR

This study estimates the charge-transfer gap in T'-RE2CuO4 and T-La2CuO4 compounds using Madelung potential calculations, revealing a decrease in gap size with larger rare-earth ions, which correlates with increased conductivity.

Contribution

The paper provides the first systematic estimation of the charge-transfer gap in T'-RE2CuO4 compounds using Madelung potential calculations, linking ionic size to electronic properties.

Findings

Charge-transfer gap decreases linearly with ionic radius of RE.

Gap values range from 12.24 eV for T'-Tm2CuO4 to 9.90 eV for T'-La2CuO4.

Results support the correlation between smaller gaps and higher conductivity.

Abstract

T'-RE2CuO4 (RE: rare-earth element), after appropriate "reduction", has fairly high conductivity and also exhibits clear Fermi edge in photoemission spectroscopy. To clarify the origin of conductivity in the T' mother compounds, we evaluated the unscreened charge-transfer gap for T'-RE2CuO4 and T-La2CuO4. The value of charge-transfer gap for T'-compounds almost linearly decreases with increasing the ionic radius of RE from 12.24 eV for T'-Tm2CuO4 to 9.90 eV for T'-La2CuO4. The results qualitatively explain metallic conductivity in T'-RE2CuO4 for large RE.