Regensburg 2022 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 2: Nanotubes, Nanoribbons and Graphene
TT 2.14: Vortrag
Montag, 5. September 2022, 13:00–13:15, H22
Ising superconductivity induced from valley symmetry breaking in twisted trilayer graphene — •Tobias Stauber1 and Jose Gonzalez2 — 1Instituto de Ciencia de Materiales de Madrid, CSIC — 2Instituto de Estructura de la Materia, CSIC
We show that the e-e interaction induces a strong breakdown of valley symmetry in twisted trilayer graphene, just before the superconducting instability develops in the hole-doped material. We analyze this effect by means of an atomistic self-consistent Hartree-Fock approximation, which is a sensible approach as the Fock part becomes crucial to capture the breakdown of symmetry. This effect allows us to reproduce the experimental observation of the Hall density, including the reset at 2-hole doping. Moreover, the breakdown of valley symmetry has important consequences for the superconductivity, as it implies a reduction of symmetry down to the C3 group. This leads to spin-splitting with respect to the two different valleys, suggesting Ising superconductivity and leading to a Paul-violation with a factor 2-3 as seen in experiments [1]. We also find spin-layer locking which might explain the strong-coupling limit of superconductivity seen in general moiré-samples. We stress that the breakdown of symmetry down to C3 and subsequent spin-valley and spin-layer locking may be shared by other materials with valley symmetry breaking.
[1] J. González and T. Stauber, arXiv:2110.11294