Non-Hermitian topology and skin effect in Co-graphene nanoribbons*

Recently, non-Hermitian effects on the topology of quantum materials have attracted much interest due to their unusual properties compared to Hermitian topology. A distinct character of non-Hermitian topology is that it breaks the limitation of the requirement of a real band gap. The system may not have a gap in the real spectrum but could still be topological as long as a point gap in the complex spectrum exists. However, the way of realizing non-Hermitian topology in a realistic 1D condensed matter system is still missing. In this work, we study a particular type of graphene nanoribbon with cobalt adatoms (Co-GNR). Due to many-electron interactions, the Hamiltonian characterizing quasiparticle excitations becomes non-Hermitian. The strong spin-orbit coupling brought by the cobalt atoms induces non-trivial non-Hermitian topology in the GW quasiparticle band structure. We extract effective tight-binding parameters with a Wannier function basis and unveil the non-Hermitian skin effect in Co-GNR.