Sujay Ray

working with
Prof. Tanmoy Das

Wannier pairs in the superconducting twisted bilayer graphene
and related systems


Abstract:

The twisted bilayer graphene (TBG) presents a new setting where superconductivity emerges on the flat bands whoseWannier wavefunctions spread over many graphene unit cells, forming the so-called Moir ́e pattern. To unravel how Wannier states form Cooper pairs, we study the interplay between electronic, structural, and pairing instabilities in TBG. For comparisons, we also study graphene on boron-nitride (GBN) possessing a different Moir ́e pattern, and single-layer graphene (SLG) without a Moir ́e pattern. We compute the pairing eigenvalues and eigenfunctions by solving a linearized superconducting gap equation, where the spin-fluctuation mediated pairing potential is evaluated from materials specific tight- binding band structures. We find an extended s-wave as the leading pairing symmetry in TBG. In contrast, GBN assumes a p + ip-wave and SLG has the d + id-wave symmetry. Moreover, while p + ip, and d+id pairings are chiral, and nodeless, but the extended s-wave channel possesses accidental nodes.


Reference:

S. Ray, J. Jung, and T. Das, Wannier pairs in the superconducting twisted bilayer graphene and related systems, Phys. Rev. B 99, 134515 (2019)

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