Preserving orbital order in a layered manganite by ultrafast hybridized band excitation

TL;DR

This study demonstrates that ultrafast hybridized band excitation can preserve orbital order in layered manganites, revealing a distinct charge transfer mechanism that differs from conventional photoinduced transitions.

Contribution

It uncovers a new charge transfer process ($d^{0} o d^{1}L$) in layered manganites under ultrafast excitation, diverging from typical $d^{1}d^{0} o d^{0}d^{1}$ transitions.

Findings

Orbital order is only slightly diminished under ultrafast excitation.

A new charge transfer mechanism ($d^{0} o d^{1}L$) is observed.

Ultrafast methods reveal different dynamics than traditional optical excitation.

Abstract

In the mixed-valence manganites, a near-infrared laser typically melts the orbital and spin order simultaneously, corresponding to the photoinduced $d^{1}d^{0}$ $\xrightarrow{}$ $d^{0}d^{1}$ excitations in the Mott-Hubbard bands of manganese. Here, we use ultrafast methods -- both femtosecond resonant x-ray diffraction and optical reflectivity -- to demonstrate that the orbital response in the layered manganite Nd$_{1-x}$Sr$_{1+x}$MnO$_{4}$ ($\it{x}$ = 2/3) does not follow this scheme. At the photoexcitation saturation fluence, the orbital order is only diminished by a few percent in the transient state. Instead of the typical $d^{1}d^{0}$ $\xrightarrow{}$ $d^{0}d^{1}$ transition, a near-infrared pump in this compound promotes a fundamentally distinct mechanism of charge transfer, the $d^{0}$ $ \xrightarrow{}$ $d^{1}L$, where $\it{L}$ denotes a hole in the oxygen band. This novel finding may pave a new avenue for selectively manipulating specific types of order in complex materials of this class.