Robust Flat-Magnetoresistivity in a 3D Nodal Flat-band Semimetal

Electrical resistivity quantifies a material's ability to impede the flow of electric current. The resistance in an external magnetic field (the magnetoresistance, MR) may increase (positive MR) or decrease (negative MR), with extremely rare instances of remaining unchanged, particularly in an order of decades of tesla. Here, we report the exotic MR observed in a high-quality Fe3Ga single crystal. Particularly, we discovered a flat-MR in the 3D nodal flat-band semimetal Fe3Ga, which robustly unchanged under the magnetic field as strong as 33 teslas. Furthermore, we found the 3D nodal flat-band induced planar Hall effect (PHE) and planar longitudinal magnetoresistance (PLMR) precisely twice the amplitude depicted by the prevailing chiral anomaly theory. Our findings open a new path to the understanding of the exotic MR in 3D nodal flat-band but also demonstrate that the high-quality Fe₃Ga acts as an ideal platform for innovating advanced quantum devices.