katch wreck"We observe a prominent high-frequency hydrodynamic bipolar-plasmon resonance and a weaker low-frequency energy-wave resonance of the Dirac fluid in ultraclean graphene. The hydrodynamic bipolar plasmon is characterized by the antiphase oscillation of massless electrons and holes in graphene. The hydrodynamic energy wave is an electron-hole sound mode with both charge carriers oscillating in phase and moving together."
https://www.nature.com/articles/s41586-022-05619-8#:~:text=We%20observe%20a,and%20moving%20together.
Observation of hydrodynamic plasmons and energy waves in graphene - Nature
By using new on-chip terahertz spectroscopy techniques to measure the absorption spectra of a graphene microribbon as well as the energy waves close to charge neutrality, hydrodynamic collective excitations are observed.