A Quantum Framework for Negative Magnetoresistance in Multi-Weyl Semimetals

We develop a quantum theory of negative magnetoresistance in multi-Weyl semimetals in the E ∥ B configuration, where the chiral anomaly is activated. The magnetotransport response is governed by Landau quantization and the emergence of multiple chiral Landau levels associated with higher-order Weyl nodes. These anomaly-active modes have unidirectional dispersion fixed by the node's monopole charge and dominate charge transport. As the magnetic field increases, individual chiral branches successively cross the Fermi energy, producing discrete slope changes in the longitudinal conductivity and a step-like negative magnetoresistance. This quantized evolution provides a direct experimental signature of multi-Weyl topology. Bulk Landau levels contribute only at very low fields due to strong disorder scattering and do not affect the anomaly-driven regime. Our results establish a unified, fully quantum-mechanical framework in which negative magnetoresistance arises from the discrete Landau-quantized spectrum and microscopic impurity scattering, beyond semiclassical anomaly descriptions.