  We report that spin polarization occurs over millimeters in polycrystalline
bulk samples of chiral disilicide NbSi$_2$ and TaSi$_2$. As previously
demonstrated in the experiments using single crystals of NbSi$_2$ and TaSi$_2$,
electrical transport measurements allow detection of direct and inverse signals
associated with the chirality-induced spin polarization even in the chiral
polycrystals. The spin polarization signals also appear in nonlocal
measurements, in which charge current flows only in the area millimeters away
from the detection electrode. These data mean that the spin polarization
phenomena occur regardless of the presence of crystalline grains in the
polycrystals, indicating a robustness and resilience of the chirality-induced
spin polarization. On the basis of the experimental data, we found that the sum
rule holds for the spin transport signals. A distribution of handedness over
the samples was determined on average in the polycrystals. While the mechanism
of preserving the spin polarization over millimeters remains to be clarified,
the present study may open up prospects of spin control and manipulation over
macroscopic length scales using chiral materials.
