Electron Correlations in an Organic Dirac-Cone Material

Abstract

The Coulomb interaction among massless Dirac electrons in graphene is unscreened around the isotropic band-crossing points, causing a logarithmic velocity renormalization and a Dirac cone reshaping. In less symmetric materials possessing anisotropic Dirac cones with tilted axes, the Coulomb interaction can provide still more exotic phenomena which have not been experimentally unveiled yet. Using site-selective nuclear magnetic resonance, we find a non-uniform cone reshaping accompanied by a bandwidth reduction and an emergent ferrimagnetism in tilted Dirac cones that appear on the verge of charge ordering in an organic compound. Our theoretical analyses based on the renormalization-group approach and the Hubbard model show that these observations are the direct consequences of the long-range and short-range parts of the Coulomb interaction, respectively. The cone reshaping and the bandwidth renormalization, as well as the novel magnetism revealed here, can be ubiquitous and vital for many Dirac cone materials in general.