Quantum Femtosecond Magnetism in Strongly Correlated Electrons induced by Femtosecond Far-Infrared Pulses

There is growing evidence that femtosecond laser-induced transient polarization can be used to manipulate magnetic and electronic orders during a laser pulse. Recently we reveal a new paradigm called \textit{quantum femtosecond magnetism}---photoinduced femtosecond magnetic phase transitions driven by quantum spin flip fluctuations correlated with laser-excited inter-atomic bonding coherence. It provides the opportunity to study the non-equilibrium quantum dynamics of phase competitions in strongly correlated materials. In addition, the scheme of photo modulation of the magnetic/electronic properties of materials also provides potential candidates for industrial application. In this talk, we show our results of using femtosecond far-infrared to tune the ground state of a strongly correlated manganese oxide. A transient photo-induced coherence is introduced far below the band gap without electronic heating and inter-band transition. Such photo-induced coherence affects the spin correlations and the resonant phonon vibrational modes, which thus leads to femtosecond spin and charge dynamics. Such non-equilibrium quantum control of the magnetic/electronic order goes beyond the scope of the conventional thermal dynamics and provides new insights into correlation mechanisms in the materials.