Electronic interactions in Dirac fluids visualized by nano-terahertz spacetime interference of electron-photon quasiparticles

TL;DR

This study uses nano-terahertz spacetime interference imaging of electron-photon quasiparticles in ultraclean graphene to reveal strong electron interactions and deviations from Fermi-liquid behavior, providing a new way to probe quantum material electrodynamics.

Contribution

It introduces a novel spacetime imaging technique using THz interference patterns to directly measure polariton dynamics and electron interactions in Dirac fluids.

Findings

Uncovered significant deviations from Fermi-liquid theory in electron dynamics.

Mapped polariton group velocity and lifetime to electronic spectral properties.

Demonstrated the method's broad applicability to quantum materials.

Abstract

Ultraclean graphene at charge neutrality hosts a quantum critical Dirac fluid of interacting electrons and holes. Interactions profoundly affect the charge dynamics of graphene, which is encoded in the properties of its electron-photon collective modes: surface plasmon polaritons (SPPs). Here we show that polaritonic interference patterns are particularly well suited to unveil the interactions in Dirac fluids by tracking polaritonic interference in time at temporal scales commensurate with the electronic scattering. Spacetime SPP interference patterns recorded in tera-hertz (THz) frequency range provided unobstructed readouts of the group velocity and lifetime of polariton that can be directly mapped onto the electronic spectral weight and the relaxation rate. Our data uncovered prominent departures of the electron dynamics from the predictions of the conventional Fermi-liquid theory. The deviations are particularly strong when the densities of electrons and holes are approximately equal. The proposed spacetime imaging methodology can be broadly applied to probe the electrodynamics of quantum materials.