Nonlinear Transport Fingerprints of Tunable Fermi-arc Connectivity in Magnetic Weyl Semimetal Co 3 Sn 2 S 2

Fermi arcs (FAs) in Weyl semimetals provide a unique platform for surface-state engineering, yet directly tracking of their evolution under surface tuning remains experimentally challenging. Here we theoretically propose that nonreciprocal charge transport can serve as a direct probe of Fermi arc Lifshitz transitions (FALT). We show that different surface terminations in Co 3 Sn 2 S 2 can produce finite and highly tunable second-order nonreciprocal signals, which can be further modulated by adjusting the surface potential. Strikingly, we show that the second-order conductivity exhibits sign changes as the Fermi arc connectivity is tuned across FALT driven by gating or chemical potential variation. This behavior arises from the chiral nature of electron velocities on the FAs, and is highly sensitive to surface termination and symmetry breaking. Our findings establish nonreciprocal transport as an electrically measurable fingerprint of FALT and propose new strategies that could be directly applied in devices for in situ engineering and detecting transport properties in topological materials.