Spiral band structure hidden in the bulk chiral crystal NbSi₂

The electronic structure of chiral crystal NbSi2 is investigated using angle-resolved photoelectron spectroscopy and density-functional theory calculations. In addition to the observation of clear band dispersions over a wide energy range, unexpected spiral-shaped constant energy contours (CECs) are found at specific binding energies. The rotation direction of this spiral signal is reversed in crystals having opposite chirality, indicating that the observed CECs originate from the structural chirality. Our theoretical analysis suggests that a combination of the bulk chiral atomic arrangement and surface states that penetrate sufficiently deep into the bulk is the key to understanding the emergence of spiral CECs.