Speaker: Markus B. Raschke (University of Colorado)

Time: March 20, 2017 10:00

Place: 物理系C302报告厅

Abstract：

Many materials exhibit inhomogeneities due to domain formation, defects, and grain boundaries, as a result of competition between short-range order between atomic constituents and long-range interactions associated with magnetic or electric polarization or strain. However, the underlying microscopic electronic, lattice, and spin interactions that give rise to a range of emergent complex materials properties are yet poorly understood. I will discuss the combination of new nano-optical scanning probe techniques of tip-enhanced and scattering scanning near-field optical microscopy (s-SNOM) with different linear, inelastic, nonlinear, and ultrafast spectroscopies. By selective optical near-field coupling to electronic, lattice, and spin degrees of freedom and their symmetries this allows probing architecture of domains and heterogeneities with nanometer spatial resolution.

Specific examples include nano-imaging of the phase separation and its dynamics between metallic and different insulating phases in the metal-to-insulator transition in VO₂. The extension of tip-enhanced Raman and IR s-SNOM spectroscopy allows for vibrational and phonon nano-crystallography, e.g., for the study of finite-size effects on the ferroelectric order in BaTiO₃ nanocrystals, BiFeO_3, or organic electronics. The spatial and time-reversal symmetry selectivity of nonlinear optical interactions can access the coupled ferroelectric and antiferromagnetic nanoscale domain topology and order in multiferroics. Other examples include the multimodal imaging of the exciton and lattice degrees of freedom in transition metal dichalcognides, graphene, and topological insulator materials. Finally, I will provide an outlook based on our recent developments on femtosecond optical control for nanoscale ultrafast spatio-temporal imaging.

Bio: 

Markus Raschke is professor at the Department of Physics, Department of Chemistry, and JILA at the University of Colorado at Boulder. His research is on the development and application of new nano-scale nonlinear and ultrafast spectroscopy techniques to control the light-matter interaction on the nanoscale. These techniques allow for imaging structure and dynamics of molecular and correlated matter with nanometer spatial resolution. He received his PhD in 2000 from the Max-Planck Institute of Quantum Optics and the Technical University in Munich, Germany. Following research appointments at the University of California at Berkeley, and the Max-Born-Institute in Berlin, he became faculty member at the University of Washington in 2006, before moving with his group to Boulder in 2010. He is fellow of the Optical Society of America, the American Physical Society, and the American Association for the Advancement of Science.