2021/08/11 by Aaron Chew, Chew, Aaron, Yijie Wang +5 · 6 citations
Materials Science · Physics and Astronomy · #Bilayer graphene #Condensed matter physics #Excited state #FOS: Physical sciences #Graphene #Graphene research and applications #Hamiltonian (control theory) #MAJORANA #Pairing #Physics #Quantum and electron transport phenomena #Quantum mechanics #Singlet state #Spin (aerodynamics) #Superconductivity #Superconductivity (cond-mat.supr-con) #Topological Materials and Phenomena #Topology (electrical circuits) #cond-mat.supr-con
paper · pdf · doi:10.48550/arxiv.2108.05373
published in arXiv (Cornell University) (Cornell University) · 6+31 pages, 3+8 figures
arxiv created 2021/08/11 · openalex publication_date 2021/08/11 · arxiv updated 2021/08/13 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
We show that introducing spin-singlet or spin-triplet superconductivity into twisted bilayer graphene induces higher-order topological superconductivity. C2zT-protected corner states of Majorana Kramers pairs appear at the boundary between domains with opposite signs of pairing, and zero modes materialize in Abrikosov vortices. The topology of the superconducting phase originates from the anomaly [1] -- the absence of a lattice support -- of the single-valley band structure of twisted bilayer graphene, which is protected by C2zT and the particle-hole symmetry \cal P. We prove that any pairing (spin-singlet or spin-triplet) term preserving valley-U(1), spin-SU(2), time-reversal, C2zT, and \cal P must drive the system into a higher-order topological superconductor phase. Here spin-SU(2) is the global spin-SU(2) for the singlet pairing and a combination of two SU(2)'s in the two valleys for the triplet pairing. Using a Dirac Hamiltonian, we demonstrate the existence of corner modes and confirm this with numerical calculations. These corner states are stable even if the approximate particle-hole symmetry \cal P is weakly broken, which is true in experimental setups. Finally, we suggest an experiment to detect the topological superconductivity: by observing the fractional Josephson effect in a TBG-TSC Josephson system.