Speaker: Yue Cao, Brookhaven National Laboratory
Program Description
Magnetic correlations are the fundamental building blocks of magnetism, and are suspected by many to be the driving force behind such exotic phenomenon as high Tc superconductivity. The marriage between the Free Electron Laser (FEL) and inelastic X-ray spectroscopy has allowed a unique opportunity to directly map the magnetic correlations in the transient photo-excited states, as a function of momentum transfer and energy exchange.
In this talk, we will discuss our first implementation of time-resolved resonant inelastic X-ray scattering (tr-RIXS) at LCLS. We photo-dope a model antiferromagnetic Mott insulator Sr2IrO4, and find that the non-equilibrium state 2 ps after the excitation hosts strong two-dimensional (2D) in-plane Néel correlations, which recover within a few picoseconds. Meanwhile, the three-dimensional (3D) long-range magnetic order restores on a fluence-dependent timescale of a few hundred picoseconds. The non-thermal nature of the 2D magnetic correlations put stringent constraints on possible theoretical descriptions of the transient state, and invites experimental explorations into the sub-picosecond regime.
Bio
Yue Cao received his Bachelor of Science from Tsinghua University, China in 2007 and his PhD from University of Colorado at Boulder in 2014. Yue moved to the X-ray Scattering Group, CMPMSD at Brookhaven National Laboratory as a postdoc in July 2014. His primary research interest now is to use elastic/inelastic X-ray scattering to study the ordering and excitations in transition metal oxides with strong electron correlations, with a special focus on the transient behavior of these orders and excitations under controlled perturbations.
