Stronger-correlated superconductivity in magic-angle twisted trilayer graphene

2021 Journal Club for Condensed Matter Physics  
Since the discovery of superconductivity in magic-angle twisted bilayer graphene (MA-TBG) featured in JCCM April 2018 (and revisited by the JCCM hopefully not one-toomany times since), strongly interacting phenomena have been discovered in a growing array of other "moire materials," from twisted bilayers of bilayers to ABC-stacked graphene on hBN. But despite this proliferation, only MA-TBG has displayed unambiguous and widely reproducible evidence for superconductivity. The featured
more » ... featured experimental results on magicangle twisted trilayer graphene (MA-TTG) now add a new superconducting entry to the list. With the mechanism for superconductivity in MA-TBG still unresolved, comparison of these two materials offers some intriguing new constraints on which aspects of the physics we should be focusing on. In the featured theory paper, Khalaf et al. first considered a graphene trilayer with a relative twist of θ between layers 1-2 and twist −θ between layers 2-3, so that the whole structure has a mirror symmetry M z exchanging the two outer layers. The M z symmetry causes the spectrum to decouple into two sectors; the M z -odd component has a Dirac spectrum with the velocity of graphene, while the two M z -even states hybridize into a pair of flat-bands in exact analogy with MA-TBG. The rough picture is thus "TTG = MLG + TBG," and due to the high velocity and low DOS of the MLG-like Dirac spectrum, its effect on the interaction physics of the TBG-like flat-bands is expected to be rather small.
doi:10.36471/jccm_january_2021_02 fatcat:v7h7su3kqfc37ayknugfpxejxi