Ultrafast surface melting of orbital order in La0.5Sr1.5MnO4

TL;DR

This study investigates how ultrafast laser pulses induce surface melting of orbital order in La0.5Sr1.5MnO4, revealing heterogeneous dynamics where the surface disorder increases while the bulk shows increased correlation length.

Contribution

It provides the first detailed measurement of surface-specific orbital order dynamics, distinguishing surface melting from bulk behavior in a layered manganite.

Findings

Surface orbital order melts heterogeneously after photoexcitation.

Surface correlation length decreases, bulk correlation length increases.

Loss of order involves incoherent processes and polaron formation.

Abstract

Understanding how light modifies long-range order in quantum materials is key to improving our ability to control functionality. However, this is challenging if the response is heterogeneous. Here we address the most common form of light-induced heterogeneity, surface melting, and measure the dynamics of orbital order in the layered manganite, La0.5Sr1.5MnO4. We isolate the surface dynamics from the bulk by measuring the orbital truncation rod as well as orbital Bragg peak. After photoexcitation, the orbital Bragg peak shows an unusual narrowing, which suggests an increase in the correlation length in the probed volume. In contrast, the correlation length at the surface decreases. These differences can be reconciled if the material is heterogeneous, and light melts a less ordered surface. By isolating the surface response, we determine that the loss of long-range order is an incoherent process, which is likely accompanied by the formation of local polarons.