Invited Paper SA+MI-ThM10
Study of Photo-induced Dynamics in Quantum Materials using Femtosecond Time-resolved X-ray Scattering
Thursday, October 25, 2018, 11:00 am, Room 202A
It remains a great challenge to characterize and understand photo-induced dynamics in quantum materials when it is driven out-of-equilibrium by ultrafast photon pulses. Time-resolved x-ray scattering, enabled by x-ray free electron laser, can track the time-evolution of the magnetic, charge, and lattice degrees of freedom with femtosecond time resolution, providing new insights into the photo-induced dynamics. In this presentation, I will first highlight photo-induced dynamics of spin and charge orders in striped nickelate. The strong coupling between spin and charge orders still survives, despite that both orders have been strongly suppressed by photo-excitations [1,2]. In addition, by resonantly pumping a bond-stretching phonon using mid-IR pulses, we observed lattice-driven dynamics that is different from hot-electron-driven dynamics induced by optical pumping across the band gap [3]. Then, I will discuss phenomena associated with coherent lattice oscillations by highlighting the measurement of atomic displacement of a coherent A1g mode in an iron-based superconductor BaFe2As2, which can be correlated with accompanied electronic variations [4]. In particular, a quantitative “lock-in” comparison between electronic band structure obtained by time-resolved ARPES and the measured atomic displacements allows us to directly obtain orbital-specific electron-phonon coupling strength without any prior assumption of the electronic band structures [5]. Finally, I will showcase a proof-of-principle time-resolved RIXS experiment on CDW ordered 1T-TiSe2 as an outlook for the future time-resolved x-ray scattering experiment in the next generation x-ray free electron laser, such as the LCLS-II.
1. W. S. Lee et al.. Phase fluctuations and the absence of topological defects in photo-excited charge ordered nickelate. Nature Communications 3, 838 (2012).
2. Y. D. Chuang, W. S. Lee et al., Real-Time Manifestation of Strongly Coupled Spin and Charge Order Parameters in Stripe-Ordered La1.75Sr0.25NiO4 Nickelate Crystals Using Time-Resolved Resonant X-Ray Diffraction. Phys. Rev. Lett. 110, 127404 (2013).
3. W. S. Lee et al., Non-equilibrium Lattice-driven Dynamics of Stripes in Nickelates using Time-Resolved X-ray Scattering. Phys. Rev. B 95, 121105(R) (2017).
4. S. Gerber, et al., Direct characterization of photo-induced lattice dynamics in BaFe2As2. Nature Communication 6, 7377 (2015).
5. S. Gerber, S.-L. Yang et al., Femtosecond electron-phonon lock-in via photoemission and x-ray free-electron laser. Science 357, 71 (2017).