Nonthermal breaking of magnetic order via photogenerated spin defects in the spin-orbit coupled insulator Sr3Ir2O7

In many strongly correlated insulators, antiferromagnetic order competes with exotic and technologically relevant phases, like superconductivity. While control of spin order is critical to stabilize different functional states, elucidating the mechanism of laser-induced demagnetization in complex oxides remains a challenge. It is unknown if the optical pulse can quench magnetization nonthermally or if it instead only acts as a heat source. Here, we use ultrafast, broadband, optical spectroscopy to track the responses of the electronic, lattice, and spin degrees of freedom and their relation to antiferromagnetism in the strongly spin-orbit coupled insulator Sr3Ir2O7. We find that magnetization can be rapidly and strongly suppressed on a sub-150 fs timescale. At low excitation fluences, the magnetic recovery is fast; however, the recovery time increases dramatically with the magnitude of demagnetization. At the same time, we show that the lattice, evidenced through the A(g) phonon frequencies, appears to remain below T-N, suggesting that the system remains nonthermal during the optical modulation of spin order. We suggest that photogenerated spin defects are responsible for the long-lived demagnetized state and discuss its implications for optical control of solids.

Automated summary

This study investigates the response of strongly spin-orbit coupled insulator Sr3Ir2O7 to laser-induced demagnetization using ultrafast, broadband, optical spectroscopy. The results show that magnetization can be rapidly and strongly suppressed within sub-150 fs timescale, and the recovery time increases with the magnitude of demagnetization. Additionally, the lattice remains in a nonthermal state during the optical modulation of spin order, suggesting the presence of photogenerated spin defects responsible for the long-lived demagnetized state.