Correlating Quasi-Electron Relaxation with Quantum Femtosecond Magnetism in the Order Parameter Dynamics of Insulating Manganites

Femtosecond (fs)-resolved simultaneous measurements of charge and spin dynamics reveal the coexistence of two different quasi-particle excitations in colossal magneto-resistive (CMR) manganites, with {\em fs} and {\em ps} relaxation times respectively. Their populations reverse size above a {\em photoexcitation-intensity-threshold} coinciding with a “sudden” antiferro-to-ferromagnetic switching during $<$100 fs laser pulses. We present evidence that fast, metallic, mobile quasi–electrons dressed by {\em quantum spin fluctuations} coexist with slow, localized, polaronic charge carriers in non-equilibrium phases. This may be central to CMR transition and leads to a laser-driven charge reorganization simultaneously with quantum fs magnetism via an emergent quantum-spin/charge/lattice transient coupling.