MSE Virtual Seminar: Peter Abbamonte, University of Illinois at Urbana Champaign
Measuring the charge dynamics in quantum materials with low-energy electron scattering
University of Illinois, Urbana, IL, USA
Nearly everything we know about quantum materials comes from spectroscopy experiments that measure electron dynamics at the energy scale of millielectron volts (meV). Some of the most successful techniques are angle-resolved photoemission (ARPES), scanning tunneling microscopy (STM), and inelastic neutron scattering (INS). The first two techniques measure the quantum dynamics of individual electrons, notably the energy band structure. The third measures the spin collective modes, notably the magnon excitations that define the magnetization dynamics of a material. Together, these methods form the foundation for progress in quantum materials in the 21st century.
Strangely, there has never been an equivalent probe of the charge collective modes. These include well-known excitations like plasmons, phonons, and excitons, as well as more exotic bosons such as axion and Higgs particles. In this talk, I will describe our group’s efforts to measure charge collective modes in quantum materials using momentum-resolved electron energy-loss spectroscopy (M-EELS), which provides energy and momentum resolution comparable to ARPES and INS techniques. I will highlight our biggest successes so far, which include demonstration of a Bose condensate of excitons in TiSe2, as well as and a quantized dynamic charge response in the “strange metals” Bi2Sr2CaCu2O8+x and Sr2RuO4. I will close by discussing prospects for the future.
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