Correlation effects in multilayer graphene

Graphene is a remarkable material, just one carbon atom thick. Systems composed of a few layers of graphene, stacked together in a special arrangement or twisted relative to each other, have proven to be an astonishingly fertile ground to study correlated phases of matter, including correlated insulators, superconductors, and topological phases, with unprecedented control and new probes, not available in three-dimensional materials.

When two layers of graphene are stacked with a special "magic" twist angle relative to each other, the active electronic bands become anomalously narrow, dramatically enhancing the effect of correlations. A small electronic dispersion can be achieved also without a relative twist, by applying a perpendicular electric field to multilayers of graphene stacked in certain ways. When these narrow bands are partially filled with electrons, a cascade of electronic phase transitions results. In between the different correlated phases, superconductivity was discovered. The theoretical challenge is to model this fascinating class of systems, developing new methods to treat the problem non-perturbatively and to predict the different correlated metallic and insulating states that emerge. Particularly interesting is the possibility of unconventional pairing, mediated by purely repulsive electron-electron Coulomb interactions. 

Selected Publications:

  • "Imaging Chern mosaic and Berry-curvature magnetism in magic-angle graphene", Sameer Grover, Matan Bocarsly, Aviram Uri, Petr Stepanov, Giorgio Di Battista, Indranil Roy, Jiewen Xiao, Alexander Y. Meltzer, Yuri Myasoedov, Keshav Pareek, Kenji Watanabe, Takashi Taniguchi, Binghai Yan, Ady Stern, Erez Berg, Dmitri K. Efetov, Eli Zeldov, arXiv:2201.06901.

  • "In-plane orbital magnetization as a probe for symmetry breaking in strained twisted bilayer graphene", Ohad Antebi, Ady Stern, Erez Berg, arXiv:2112.14785.

  • "Unconventional superconductivity in systems with annular Fermi surfaces: Application to rhombohedral trilayer graphene", Areg Ghazaryan, Tobias Holder, Maksym Serbyn, Erez Berg, Phys. Rev. Lett. 127, 247001 (2021) (Editor's suggestion). 
  • "Inter-valley coherent order and isospin fluctuation mediated superconductivity in rhombohedral trilayer graphene", Shubhayu Chatterjee, Taige Wang, Erez Berg, Michael P. Zaletel, arXiv:2109.00002.
  • Theory of correlated insulators and superconductivity in twisted bilayer graphene, Gal Shavit, Erez Berg, Ady Stern, Yuval Oreg, Phys. Rev. Lett. 127, 247703 (2021).
  • "Fermionic Monte Carlo study of a realistic model of twisted bilayer graphene", Johannes S. Hofmann, Eslam Khalaf, Ashvin Vishwanath, Erez Berg, Jong Yeon Lee, arXiv:2105.12112; Accepted to Phys. Rev. X (2022).
  • "Half and quarter metals in rhombohedral trilayer graphene", Haoxin Zhou, Tian Xie, Areg Ghazaryan, Tobias Holder, James R. Ehrets, Eric M. Spanton, Takashi Taniguchi, Kenji Watanabe, Erez Berg, Maksym Serbyn, Andrea F. Young, Nature 598 429-433 (2021)
  • "Spin-polarized superconductivity: Order parameter topology, current dissipation, and multiple-period Josephson effect", Eyal Cornfeld, Mark S. Rudner, and Erez Berg, Phys. Rev. Research 3, 013051 (2021).
  • "Entropic evidence for a Pomeranchuk effect in magic-angle graphene", Asaf Rozen, Jeong Min Park, Uri Zondiner, Yuan Cao, Daniel Rodan-Legrain, Takashi Taniguchi, Kenji Watanabe, Yuval Oreg, Ady Stern, Erez Berg, Pablo Jarillo-Herrero, and Shahal Ilani, Nature 592, 214–219 (2021).
  • "Isospin Pomeranchuk effect and the entropy of collective excitations in twisted bilayer graphene", Yu Saito, Fangyuan Yang, Jingyuan Ge, Xiaoxue Liu, Kenji Watanabe, Takashi Taniguchi, J.I.A. Li, Erez Berg, Andrea F. Young, Nature 592, 220-224 (2021).
  • "Cascade of Phase Transitions and Dirac Revivals in Magic Angle Graphene",  Uri Zondiner, Asaf Rozen, Daniel Rodan-Legrain, Yuan Cao, Raquel Queiroz, Takashi Taniguchi, Kenji Watanabe, Yuval Oreg, Felix von Oppen, Ady Stern, Erez Berg, Pablo Jarillo-Herrero, Shahal Ilani, Nature, 582, 203 (2020).