Extended Data Fig. 8: Fitting the current dependent measurements.

The ratio of the second to first harmonic resistances, \({R}_{{xx}}^{2\omega }/{R}_{{xx}}^{1\omega },\) at 10 K and zero applied magnetic field, plotted as a function of the applied current I for the three helical devices with pitch lengths L = 0.5, 1.0 and 2.0 μm, as labelled. Error bars indicate the standard error across 10 data points around B = 0, dominated by the noise in the \({R}_{{xx}}^{2\omega }\) measurement. The linear fits give a value for Γ of each device via the gradient, which is plotted as a function of L in the inset.