Longitudinal magnetoresistance was measured at strain set points for field parallel the current along the a axis. In addition to the results reported in Fig. 3 (A and B), two other crystals were measured (shown in fig. S5). For all crystals, we measured a positive magnetoconductance after a small dip in the magnetoconductance for very low fields. The small dip in longitudinal magnetoconductance near zero field is commonly observed in other materials that exhibit chiral anomaly. Its origin is not completely understood. Two possibilities are weak antilocalization effect and the classical Lorentz longitudinal magnetoresistance in anisotropic metals that saturates when ωcτ ~ 1. The positive magnetoconductance was suppressed for strains as low as 0.02% away from ϵmin for both compressive and tensile strains.

NLMR is only observed for magnetic fields finely aligned to the current, IBa. We aligned our apparatus such that the magnetic field is parallel to the a axis of the sample. The apparatus itself was machined to within 20-μm precision so that the plane of the edge of apparatus can be very precisely aligned to the magnetic field (<1°). The primary opportunity for misalignment is the crystal being misaligned within the plane of the apparatus. To minimize misalignment along this axis, we used an optical microscope to inspect and adjust the alignment of the crystal after it was placed in glue on the apparatus. The glue adhering the crystal dried slowly enough to allow time for alignment adjustment under the optical microscope. We found that we can frequently align crystals within 1° of alignment using this simple technique.

To verify that the crystal and apparatus were fully aligned with magnetic fields, we constructed a strain apparatus on a Quantum Design DynaCool single-axis rotation puck (as shown in fig. S6A). We tuned ϵaa to ϵmin, which we know from Fig. 3 will have the strongest NLMR response. We then measured longitudinal magnetoresistance for several angles between field and a axis, from −1.0° to +0.5° in increments of 0.25° (shown in fig. S6B). We found that the NLMR was only observed for alignments better than 1.0°, which is consistent with other results (28). Because NLMR is not observed for misalignments 1° or greater even for ϵaa = ϵmin, the observation of NLMR is evidence that our crystals are aligned to within 1° of accuracy or less.

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