Date(s) - Mar 3 2017
11:00 AM - 12:00 PM
Shasta Room, Bldg. 40, Room 361
Robert A. Kaindl
Materials Sciences Division, E. O. Lawrence Berkeley National Laboratory, Berkeley, CA
Ultrafast Terahertz and XUV ARPES Studies of
Complex Materials Dynamics
In this talk I will discuss the application of ultrashort light pulses – from terahertz (THz) to extreme-ultraviolet (XUV) – to the study of vibrational coupling and emergent correlations in complex materials. Transition-metal oxides, in particular, exhibit an intriguing self-organization of charges into nanoscale “stripes”, whose driving forces and role in high-Tc superconductivity remain unresolved. We will first present transient THz experiments that capture the initial steps of vibrational symmetry breaking and charge ordering in stripe-phase nickelates, dynamically revealing the underlying electronic and structural coupling. The second part will cover our development of ultrafast angle-resolved photoemission spectroscopy (ARPES) with XUV pulses at 50-kHz repetition rate and its application to tracking electronic dynamics across momentum space. The high XUV flux enables rapid band mapping and sensitive measurements that access e.g. the crossover from light-induced perturbation to melting of charge density waves. In particular, we will discuss studies of the semiconducting transition-metal dichalcogenide MoSe2 that map out the inter-valley scattering and relaxation dynamics. Distinct excitation-dependent and dynamical energy shifts are observed that directly reveal excitonic signatures of band gap excitons in the ARPES spectra.