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Geometric and conventional contribution to superfluid weight in twisted bilayer graphene | | Xiang Hu
; Timo Hyart
; Dmitry I. Pikulin
; Enrico Rossi
; | | Date: |
17 Jun 2019 | | Abstract: | By tuning the angle between graphene layers to specific "magic angles" the
lowest energy bands of twisted bilayer graphene (TBLG) can be made flat. The
flat nature of the bands favors the formation of collective ground states and,
in particular, TBLG has been shown to support superconductivity. When the
energy bands participating in the superconductivity are well-isolated, the
superfluid weight scales inversely with the effective mass of such bands. For
flat-band systems one would therefore conclude that even if superconducting
pairing is present most of the signatures of the superconducting state should
be absent. This conclusion is at odds with the experimental observations for
TBLG. We calculate the superfluid weight for TBLG taking into account both the
conventional contribution and the contribution arising from the quantum
geometry of the bands. We find that both contributions are larger than one
would expect treating the bands as well-isolated, that at the magic angle the
geometric contribution is larger than the conventional one, and that for small
deviations away from the magic angle the conventional contribution is larger
than the geometric one. Our results show that, despite the flatness of the
bands the superfluid weight in TBLG is finite and consistent with experimental
observations. We also show how the superfluid weight can be tuned by varying
the chemical potential and the twist angle opening the possibility to tune the
nature of the superconducting transition between the standard BCS transition
and the Berezinskii-Kosterlitz-Thouless transition. | | Source: | arXiv, 1906.7152 | | Services: | Forum | Review | PDF | Favorites | |
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