Measuring the charge dynamics in quantum materials with low-energy electron scattering

04/23/2021 - 3:30pm to 4:30pm
Speaker(s) / Presenter(s): 
Peter Abbamonte (UIUC)
Type of Event (for grouping events):

Host: Kaul


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 TiSe 2 , as well as and a quantized dynamic charge response in the “strange
metals” Bi 2 Sr 2 CaCu 2 O 8+x and Sr 2 RuO 4 . I will close by discussing prospects for the future.
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