Nonlinear transport fingerprints of tunable Fermi-arc connectivity in magnetic Weyl semimetal Co$_3$Sn$_2$S$_2$

Abstract

Fermi arcs in Weyl semimetals provide a unique platform for surface-state engineering, yet di rectly 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 Co3Sn2S2 can produce f inite 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 Fermi arcs, 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.

Figures (6)

• Figure 1: Schematic illustration of surface engineering strategies in Co$_3$Sn$_2$S$_2$ for controlling NCT. The device is based on a Co$_3$Sn$_2$S$_2$ single crystal, where NCT is tuned via three distinct surface engineering approaches: (i) surface termination manipulation (by substituting Sn-terminated surfaces with Co-terminated ones), (ii) surface chemical doping, and (iii) application of an external surface potential (via gating). The atomic structure of Co$_3$Sn$_2$S$_2$ is shown on the left, highlighting the stacking of S, Co, and Sn atoms.
• Figure 2: Calculated surface LDOS for various surface terminations of the Co$_3$Sn$_2$S$_2$ slab at $\mu=0.18eV$. Panels (a) and (b) correspond to Co-terminated top and bottom surfaces, respectively, while panel (c) shows the result for the Sn-terminated top surface. (d, e) FAs connectivity for slabs with symmetric (Co–Co) and asymmetric (Co–Sn) surface terminations.
• Figure 3: Anisotropic and tunable second-order nonreciprocal response in Co$_3$Sn$_2$S$_2$. (a) Angular dependence of the second-order nonlinear conductivity $\sigma_2$, calculated by numerical integration of Eq. (8) after coordinate rotation. (b) Layer-resolved contribution to the second-order conductivity at $\mu=0.18eV$, which can be tuned by applying a gate voltage to the Sn-terminated surface in (c). (d) Gate-controlled enhancement of the second-harmonic voltage $V^{2\omega}$ with increasing surface potential $V_{\mathrm{G}}$. (e) Nonreciprocal coefficient $\gamma’$ versus chemical potential $\mu$ for different temperatures and surface terminations. The signal peaks near the WPs for Co–Sn surfaces, but vanishes for symmetric Co–Co cases.
• Figure 4: Gate-tunable FALT and nonreciprocal nonlinear transport in Co$_3$Sn$_2$S$_2$. (a) Calculated second-order conductivity $\sigma_2$ as a function of the gate voltage $V_\mathrm{G}$. Distinct regimes (I, II, III) are separated by critical values of $V_\mathrm{G}$, corresponding to topological FALT. (b-d) Momentum-resolved surface LDOS on the Sn-terminated surface for representative values of $V_\mathrm{G}$. The FAs connectivity undergoes characteristic reconstructions across the three regimes, with sign changes at the transition points.
• Figure 5: (a,b) Metric dipole $\Gamma_{yy}=v_yG^{yy}$ for identical (Co-Co) vs. distinct (Co-Sn) surface terminations, The integration of asymmetric $\Gamma_{yy}$ (Co-Sn) gives the non-zero second-order conductivity. (c,d) Second-order conductivity of distinct terminations at zero bias.