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

Abstract

In the mixed-valence manganites, a near-infrared laser typically melts the orbital and spin order simultaneously, corresponding to the photoinduced $d^1{d}^0$ $\to$ $d^0{d}^1$ 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${}_4$ ($x$ = 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 $d^1{d}^0$ $\to$ $d^0{d}^1$ transition, a near-infrared pump in this compound promotes a fundamentally distinct mechanism of charge transfer, the $d^0$ $\to$ $d^{1}L$, where $L$ 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.