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.
Categories: cond-mat.str-el cond-mat.mtrl-sci