Cascade of low-energy surface phonon modes on the B-terminated EuB₆ surface

EuB₆ has emerged as a leading candidate magnetic Weyl semimetal, in which spontaneous ferromagnetic order breaks time-reversal symmetry and drives a topological phase transition accompanied by band inversion. Optical studies have extensively investigated the phonon modes associated with the B₆ octahedra, whose internal vibrations play an important role in understanding the physical properties of EuB₆. However, the low-energy phonon modes and their coupling to electrons remain largely unexplored. Here we report a cascade of low-energy phonon modes resolved on the B-terminated surface of EuB₆ prepared by low-temperature in situ cleavage. We show that defects significantly modulate the local electron–phonon coupling (EPC) strength. Moreover, a defect-pinned $\sqrt{2}\times \sqrt{2}$ short-range order emerges on the B-terminated surface, which selectively modulates the local density of states (LDOS) and the EPC strength. Our results provide insight into the interplay between low-energy surface phonons, defects, and electron–phonon coupling on the B-terminated surface of EuB₆.