Abstract
The Coulomb interaction among massless Dirac fermions in graphene is unscreened around the isotropic Dirac points, causing a logarithmic velocity renormalization and a cone reshaping. In less symmetric Dirac materials possessing anisotropic cones with tilted axes, the Coulomb interaction can provide still more exotic phenomena, which have not been experimentally unveiled yet. Here, 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 magnetic behaviour revealed here, can be ubiquitous and vital for many Dirac materials.
Highlights
The Coulomb interaction among massless Dirac fermions in graphene is unscreened around the isotropic Dirac points, causing a logarithmic velocity renormalization and a cone reshaping
Graphene is a special case of 2D massless Dirac fermions (DFs) systems, in which isotropic Dirac cones with vertical axes have the Dirac points (DPs) at symmetric points on the Brillouin zone boundary[2]
We mention that the observed non-uniform reshaping of titled Dirac cones in a-I3 should affect other physical observables at low temperature or at low magnetic field
Summary
The Coulomb interaction among massless Dirac fermions in graphene is unscreened around the isotropic Dirac points, causing a logarithmic velocity renormalization and a cone reshaping. Once the high-P phase is reached, the Dirac cones become stable against further pressurization; the gapless point is fixed at EF on varying the hopping integrals in a finite range by virtue of the 3/4-filled nature of the electronic bands, as revealed by band-structure calculations[23,25,26,33,42,43,44,45] The presence of such a phase transition in this system potentially offers the possibility to test the impact of the SR electron correlations on the behaviours of 2D massless DFs. the tilt of anisotropic Dirac cones[36] coupled with the SR and LR parts of the Coulomb interaction opens new possibilities in the physics of 2D massless DFs. For instance, it is predicted to bring about a non-uniform reshaping of titled cones[46], novel non-Fermi liquid behaviours near the quantum critical point[16,17], where two DPs merge[47,48], enhanced shot noise for quantum transport[49] and anomalous charge/spin textures inside the unit cell[48,50]. These experimental and theoretical investigations demonstrate that a-I3 under P is an intrinsically interacting 2D massless DF system, in which both the LR and SR parts of the Coulomb interaction strongly influence the electronic behaviours
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