A spin-polarized state is examined under charge current at room temperature without magnetic fields in chiral disilicide crystals ${\mathrm{NbSi}}_2$ and ${\mathrm{TaSi}}_2$. We found that a long-range spin transport occurs over ten micrometers in these inorganic crystals. A distribution of crystalline grains of different handedness is obtained via location-sensitive electrical transport measurements. The sum rule holds in the conversion coefficient in the current-voltage characteristics. A diamagnetic nature of the crystals supports that the spin polarization is not due to localized electron spins but due to itinerant electron spins. A large difference in the strength of antisymmetric spin-orbit interaction associated with $4d$ electrons in Nb and $5d$ ones in Ta is oppositely correlated with that of the spin polarization. A robust protection of the spin polarization occurs over long distances in chiral crystals.

• Received 9 June 2021
• Accepted 22 July 2021

DOI:https://doi.org/10.1103/PhysRevLett.127.126602