Disorder-mediated linear and nonlinear magnetotransport in the charge-density-wave material Ta2NiSe7

We report disorder-mediated first-order linear and higher-order nonlinear (magneto-)transport of Ta2NiSe7 (TNS) in the charge-density-wave (CDW) regime. CDW transition temperature (TCDW) and carrier density are proportional and inversely proportional to residual resistance ratio of samples, respectively. Such relation helps to understand the unique CDW order therein. High-TCDW TNS exhibits negative first-harmonic magnetoresistance (MR1ω) under a magnetic field (B) parallel to the direction of alternating current (Iω), which may arise from the anomalous velocity induced by the Berry curvature of three-dimensional topological bands near the Fermi level. As TCDW drops, a positive-to-negative MR1ω transition is observed with decreasing perpendicular B, which is likely due to the contribution of Zeeman effect on current pathways in the disordered system. Moreover, interestingly, the second-harmonic nonlinear signals are suppressed, while the third-harmonic signals are significant and sensitive to both B and TCDW. Such observations, together with scaling analysis, suggest the quantum geometry quadrupole at play and the modulation of disorder on third-order nonlinearity. Our results pave an avenue for tailoring distinct-order magnetoresistive phases in disordered topological materials.