Is negative longitudinal magnetoresistance a chiral-anomaly signature
In plain words
Many semimetals conduct better when a magnetic field points along the current, as the chiral anomaly predicts, but uneven current flow inside the sample (current jetting) can produce the same effect.
Precise statement
In Weyl and Dirac semimetals (Na3Bi, Cd3As2, the TaAs family, ZrTe5), the chiral anomaly predicts a longitudinal conductivity increase $\Delta \sigma_{zz} = C_a B^2$ for $E$ parallel to $B$, with $C_a$ proportional to $v^{3}\tau_v/\mu^{2}$ ($v$ Fermi velocity, $\tau_v$ intervalley scattering time, $\mu$ chemical potential from the node). Determine for each material whether the measured negative magnetoresistance follows this scaling once current jetting and inhomogeneity are excluded. An answer is a material-by-material verdict with $\tau_v$ measured independently.
What would settle it
Multi-contact potential mapping that excludes current jetting, with $C_a$ measured versus $\mu$ across gated or doped samples and compared with independently measured $\tau_v$.