Electronic structure of chiral crystal NbSi₂ examined by VUV- and SX-ARPES

Chiral crystal NbSi₂ has attracted considerable attention due to its intriguing physical phenomena arising from its chiral structure, such as chirality induced spin selectivity (CISS) effect [1] or possible Kramers Weyl Fermions [2]. Recently we have performed angle-resolved photoelectron spectroscopy (ARPES) measurement and observed spiral shaped photoelectron distribution pattern in the constant energy contours (CECs) of the valence band of the NbSi₂. We have found that the cyclic direction of these spiral shapes is related to the chirality of the crystal structure. By comparing the experimentally observed CEC patterns with those obtained by the density functional theory (DFT) calculations, we demonstrated that the observed spiral-shaped photoemission distribution patterns can be qualitatively reproduced by the calculations considering the surface state contribution [3].

In this study, to further elucidate the origin of the spiral-shaped CEC patterns, we conducted the ARPES measurements using soft X-rays (SX-ARPES) and the vacuum ultraviolet (VUV-ARPES) at the CASSIOPEE beamline at the synchrotron SOLEIL and evaluated the surface states contribution to the CEC pattern more directly. The observed clear k_z dispersion indicates that the SX-ARPES can capture the three-dimensional characteristics of the electronic states. However, although it was less distinct than that observed with VUV-ARPES, the spiral patterns were still observed with SX-ARPES. In the presentation, we will discuss the possible origin of the spiral CEC patterns observed even with the SX-ARPES.