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Interacting chiral electrons at the 2D Dirac points: a review
Michihiro Hirata1,2, Akito Kobayashi3, Claude Berthier4
1Institute for Materials Research, Tohoku University, Aoba-ku, Sendai 980-8577, Japan.
Reports on Progress in Physics. Physical Society (Great Britain)
|October 15, 2020
Summary
Interacting chiral electrons in 2D materials like graphene and organic compounds exhibit unique long-range Coulomb interactions. These interactions renormalize electron velocity and can lead to mass generation, offering insights into condensed-matter physics.
Area of Science:
- Condensed-matter physics
- Materials science
- Quantum mechanics
Background:
- Chiral electrons, such as Dirac and Weyl fermions, in 2D graphene and 3D topological semimetals present unique physical phenomena.
- The Coulomb interaction between these chiral electrons is unscreened and long-ranged near charge-neutrality, unlike in conventional materials.
- This long-range interaction in graphene causes anomalous Fermi velocity renormalization and Dirac cone reshaping, with potential for excitonic condensation and mass generation.
Purpose of the Study:
- To review recent progress in understanding interacting chiral electrons in two-dimensional (2D) systems.
- To highlight studies on graphene and the organic material $\alpha$-(BEDT-TTF)$_2$I$_3$ as key platforms for investigating these interactions.
- To explore the phenomena of velocity renormalization, mass generation, and electronic correlations in these materials.
Main Methods:
- Review of experimental and theoretical findings on interaction effects in graphene.
- Analysis of studies on $\alpha$-(BEDT-TTF)$_2$I$_3$, focusing on its emergent 2D massless-Dirac-fermion phase.
- Detailed examination of nuclear magnetic resonance experiments and model calculations in $\alpha$-(BEDT-TTF)$_2$I$_3$.
Main Results:
- Graphene exhibits logarithmic renormalization of Fermi velocity due to long-range Coulomb interaction, potentially leading to excitonic condensation.
- In $\alpha$-(BEDT-TTF)$_2$I$_3$, a 2D massless-Dirac-fermion phase adjacent to an insulating phase provides a platform to study these interactions.
- Nuclear magnetic resonance studies reveal anisotropic Dirac cone reshaping and precursor excitonic dynamics, influenced by long-range interactions near Dirac points.
Conclusions:
- The organic material $\alpha$-(BEDT-TTF)$_2$I$_3$ serves as a crucial testbed for studying velocity renormalization and mass generation driven by Coulomb interactions.
- These studies offer unique insights into electronic correlations and spin excitations influenced by long-range interactions in 2D chiral electron systems.
- The findings contribute to a deeper understanding of fundamental condensed-matter phenomena in low-dimensional materials.
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