Detection of chirality-induced spin polarization over millimeters in polycrystalline bulk samples of chiral disilicides NbSi2 and TaSi2

We report that spin polarization occurs over millimeters in polycrystalline bulk samples of chiral disilicide NbSi2 and TaSi2. As previously demonstrated in the experiments using single crystals of NbSi2 and TaSi2, electrical transport measurements allow detection of direct and inverse signals associated with the chirality-induced spin polarization even in the chiral polycrystals. 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.