Optical Characteristics of Charge Carrier Transfer across Interfaces between YBa$_2$Cu$_3$O$_{6+\delta}$ and La$_{0.7}$Ca$_{0.3}$MnO$_3$

TL;DR

This study uses spectral ellipsometry to investigate charge transfer at interfaces between superconducting YBCO and ferromagnetic LCMO, revealing hole transfer from YBCO to LCMO layers and demonstrating optical spectroscopy as a tool for probing buried interfaces.

Contribution

It provides the first detailed optical analysis of charge transfer mechanisms across YBCO/LCMO interfaces, highlighting the role of hole transfer and interface-induced spectral weight changes.

Findings

Spectral weight increases with YBCO layer thickness.

Spectral weight enhancement correlates with the number of interfaces.

Holes transfer from YBCO to LCMO layers, not pinned by defects.

Abstract

We report a spectral ellipsometry study of multilayers composed of superconducting YBa$_2$Cu$_3$O$_{6+\delta}$ (YBCO) and ferromagnetic La$_{0.7}$Ca$_{0.3}$MnO$_3$ in the spectral range of 0.7 - 6.5 eV. With increasing YBCO sublayer thickness, the optical spectral weight is enhanced at photon energies of 1.5 - 3.5 eV. The spectral weight enhancement is proportional to the number of interfaces of each multilayer sample, indicating its association with the interfacial electronic structure. Based on calculations in the framework of a multilayer model, we find that the shape of the interface-induced spectral weight is consistent with transfer of hole-carriers from YBCO to LCMO. Our results imply that the holes that are transferred across the interfaces accumulate in the LCMO layers, rather than being pinned by interfacial defects or annihilated by electron donors such as oxygen vacancies. Optical spectroscopy can thus serve as a non-destructive probe of charge transfer across buried interfaces in metal-oxide heterostructures.