Ultrafast electron dynamics upon above band-gap excitation in epitaxial LaFeO ₃ (001) thin films

Abstract Strong electron correlations in perovskite oxides give rise to rich and often unexpected electronic phenomena. In this study, we present a comprehensive surface-science investigation of epitaxial thin films of the charge-transfer insulator LaFeO 3 (001). The characterization includes low-energy electron diffraction, high-resolution electron energy loss spectroscopy, and photoemission spectroscopy. We map both the occupied and unoccupied electronic states using two-photon photoemission spectroscopy. Furthermore, we probe electron dynamics through an ultraviolet–ultraviolet pump-probe experiment, exciting electrons from hybridized O 2 p /Fe 3 d states to Fe minority-spin states above the band gap. Our results reveal three distinct unoccupied states, which we assign to Fe <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>t</mml:mi> <mml:mrow> <mml:mn>2</mml:mn> <mml:mi>g</mml:mi> <mml:mo stretchy="false">↓</mml:mo> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> , Fe <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>e</mml:mi> <mml:mrow> <mml:mi>g</mml:mi> <mml:mo stretchy="false">↓</mml:mo> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> , and La 5 d orbitals. Notably, the conduction band minimum exhibits a biexponential decay with time constants of 39 fs and 1100 fs, suggesting the presence of two independent decay pathways.