Competition between spin and charge excitations in graphene with long-range Coulomb interactions*

Graphene is the paradigm to study the interplay between the contact Hubbard interaction and the long-range Coulomb interaction [1]. This is mostly because of the experimental flexibility in tuning the interaction strength, for example, by forming a moiré superpotential by twisting, or by exerting strain. Despite the extensive research on the many-body physics of graphene, the spin and charge response to interactions remains largely unexplored. Here, we use the numerically exact projective quantum Monte Carlo with a maximum entropy method for analytical continuation to find the dynamical spin and charge response of strongly interacting graphene. We find that the long-range Coulomb interaction suppresses the quasi-particle nature, enhances charge-density wave excitations (CDW), and only weakly modifies the anti-ferromagnetic spin-wave excitations (AFM). We also find that long-range Coulomb interaction induces stiffer excitations in both CDW excitation and AFM excitation near Gamma point. We discuss how these predictions can be tested in an electron loss experiment.


References
[1] H.-K. Tang et al., “The role of electron-electron interactions in two-dimensional Dirac fermions,” Science, 361, 570 (2018).