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arXiv · 2509.12320

Putting a new spin on the incommensurate Kekul\'e spiral: from spin-valley locking and collective modes to fermiology and implications for superconductivity

Ziwei Wang·Glenn Wagner·Yves H. Kwan·Nick Bultinck·Steven H. Simon·S. A. Parameswaran
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Abstract

We revisit the global phase diagram of magic-angle twisted bilayer and [symmetric] trilayer graphene (MA-TBG/TSTG) in light of recent scanning tunneling microscopy (STM) measurements on these materials. These experiments both confirmed the importance of strain in stabilizing the predicted incommensurate Kekul\'{e} spiral (IKS) order near filling $|\nu|=2$ of the weakly dispersive central bands in both systems, and suggested a key role for electron-phonon couplings and short-range Coulomb interactions in selecting between various competing orders at low strain in MA-TBG. Here, we show that such interactions $\textit{also}$ play a crucial role in selecting the spin structure of the strain-stabilized IKS state. This in turn influences the visibility of the IKS order in STM in a manner that allows us to infer their relative importance. We use this insight in conjunction with various other pieces of experimental data to build a more complete picture of the phase diagram, focusing on the spectrum of low-lying collective modes and the nature of the doped Fermi surfaces. We explore the broad phenomenological implications of these results for superconductivity.

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Ziwei Wang, Glenn Wagner, Yves H. Kwan, Nick Bultinck, Steven H. Simon, S. A. Parameswaran. 2025-09-15. Putting a new spin on the incommensurate Kekul\'e spiral: from spin-valley locking and collective modes to fermiology and implications for superconductivity. https://arxiv.org/abs/2509.12320

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