Detection of chirality-induced spin polarization over millimeters in polycrystalline bulk samples of chiral disilicides NbSi$_2$ and TaSi$_2$

TL;DR

This study demonstrates that chirality-induced spin polarization occurs over millimeter scales in polycrystalline bulk samples of NbSi₂ and TaSi₂, showing robustness and potential for macroscopic spin control.

Contribution

It provides experimental evidence of millimeter-scale spin polarization in polycrystalline chiral disilicides, extending previous single-crystal findings and highlighting the phenomenon's resilience.

Findings

Spin polarization detected over millimeters in polycrystals.

Chirality-induced spin signals are robust against grain boundaries.

Sum rule for spin transport signals is validated.

Abstract

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.