Helical Luttinger liquid on the edge of a 2-dimensional topological antiferromagnet

Abstract

Helical Luttinger liquid (HLL) is a class of one-dimensional liquids with locked electron spin orientation and momentum. Boundary of a quantum spin Hall insulator is a good example of time-reversal symmetry (TRS) protected HLL, but its topological protection is compromised under finite magnetic field. Boundary HLL with broken bulk TRS belongs to a different topological class which may occur in antiferromagnets. The recently discovered van der Waals antiferromagnet (AFM) MnBi2Te4 offers rich topological band structures which critically relies on the magnetic structure and layer number. Here, we search for signatures of HLL on the edge of even-layer MnBi2Te4 thin flakes by combining magneto-transport and scanning superconducting quantum interference device microscopy. We directly image helical edge current in the AFM ground state appearing when the chemical potential was gated to the charge neutral point. Such helical edge state accompanies an insulating bulk which is topologically distinct from the ferromagnetic Chern insulator phase as revealed in a magnetic field driven quantum phase transition of the bulk. The edge conductance of the AFM order follows a power-law as a function of temperature and source-drain bias which serves as strong evidence for HLL. Such HLL scaling is robust at finite fields below the quantum critical point. The observed HLL in a layered AFM semiconductor represents a highly tunable topological matter compatible with future spintronics and quantum computation.