Experimental evidence for electron-electron interaction and spin-charge separation in graphene quantum dots

TL;DR

This study provides experimental evidence of electron-electron interactions and spin-charge separation in graphene quantum dots, revealing complex correlated phases not explained by free electron models.

Contribution

It reports the first observation of spin-charge separation in GQDs through scanning tunneling microscopy and spectroscopy in a heterostructure device.

Findings

Detection of two density waves with different velocities

Evidence of correlation-induced spin-charge separation

Gating effects on energy spectra of GQDs

Abstract

Graphene quantum dots (GQDs) can exhibit a range of spectacular phenomena such as the Klein-tunneling-induced quasibound states1-6 and Berry-phase-tuned energy spectra7-15. According to previous studies, all these interesting quantum phenomena seem to be well understood in the free electron picture1-15. However, electronic motion in the GQDs is reduced to quantized orbits by quantum confinement, which implies that the kinetic energy may be comparable to or even smaller than the Coulomb energy of the quasiparticles, possibly resulting in exotic correlated phases in the GQDs. Here we present a scanning tunneling microscopy and spectroscopy study of gate-tunable GQDs in graphene/WSe2 heterostructure devices and report for the first time the observation of electron-electron interaction and correlation-induced spin-charge separation in the GQDs. Gating allows us to precise characterize effects of the electron-electron interaction on the energy spectra of the GQDs. By measuring density of states as a function of energy and position, we explicitly uncover two density waves with different velocities in the GQDs, attributing to spin-charge separation in real space.