Direct observation of double exchange in ferromagnetic La$_{0.7}$Sr$_{0.3}$CoO$_3$ by broadband ellipsometry

TL;DR

This study uses broadband ellipsometry to observe how double exchange influences ferromagnetism in La$_{0.7}$Sr$_{0.3}$CoO$_3$, revealing spectral weight transfer and orbital mediation.

Contribution

It provides direct optical evidence of double exchange in cobaltite ferromagnets and links spectral changes to orbital-specific mechanisms.

Findings

Spectral weight shifts from 1.5 eV absorption to Drude peak during ferromagnetic transition.

Reduction in intraband kinetic energy exceeds thermal energy at T_c, emphasizing double exchange importance.

Temperature dependence suggests $t_{2g}$ orbitals mediate the double exchange process.

Abstract

We present results of our broadband ellipsometry measurements of the optical response of ferromagnetic La$_{0.7}$Sr$_{0.3}$CoO$_3$. Our data show that the ferromagnetic transition is accompanied by a transfer of optical spectral weight from an absorption band centered at 1.5 eV to a narrow component of the Drude-like peak. The associated reduction of the intraband kinetic energy is significantly larger than $k_{\rm B}T_c$, confirming that the double exchange plays a major role in the ferromagnetism of doped cobaltites. In conjunction with results of recent theoretical studies, the temperature dependence of the Drude-like peak suggests that the double exchange is mediated by $t_{2g}$ orbitals.