Tunable Unconventional Integer Quantum Hall Effect in Two-Dimensional Dirac-Weyl Systems

Two-dimensional (2D) Dirac semimetals possess intriguing properties due to their low-energy excitations behaving like Dirac fermions. A hallmark of these materials is the unconventional integer quantum Hall effect (IQHE), originating from the quantized Berry phase of Dirac fermions. Herein, using symmetry analysis, tightbinding models, and numerical calculations, we reveal 2D Dirac-Weyl fermions in inversion symmetry breaking systems that exhibit tunable unconventional IQHE. These unique 2D fermions are characterized by a pair of helical edge states related by time-reversal symmetry T, which connect the projections of a Dirac point and two separate Weyl nodes, indicating that the Dirac and Weyl points are interconnected as a whole. We show that these 2D Dirac-Weyl fermions exhibit a tunable unconventional IQHE, featuring a Hall plateau sequence shifted by three units of 2e2 h . The distance between adjacent quantized Hall plateaus can be adjusted by strain, which is a unique feature that distinguishes from what is observed in graphene. Through first-principles calculations, we identify an ideal candidate material for hosting 2D Dirac-Weyl fermions, offering a promising avenue for experimental verification. Our findings open up a door to exploring unconventional IQHE in condensed-matter systems beyond graphene.