Surface-extended Andreev bound states emerging from intrinsic surface superconductivity of PtBi${}_2$

Abstract

Intrinsic topological superconductivity remains one of the central open questions in condensed-matter physics. The three-dimensional Weyl semimetal PtBi${}_2$ has recently been shown by angle-resolved photoemission spectroscopy to host a superconducting gap that opens exclusively on its Fermi-arc surface states and exhibits a nodal structure, making it a promising platform for exploring unconventional and potentially topological superconductivity. However, despite these momentum-resolved insights, the real-space spectroscopic signatures of unconventional superconductivity in PtBi${}_2$ remain unclear. Here, using scanning tunneling microscopy and spectroscopy, we reveal a sizable and spatially homogeneous gap ($\Delta >10\mathrm{meV}$) on atomically pristine terraces of PtBi${}_2$. Within this gap, we detect surface-extended in-gap states exhibiting pronounced atomic-scale spatial modulation. Analysis of the tunneling spectra indicates that these states are most consistently interpreted as Andreev bound states within a superconducting gap. Further phenomenological modeling shows that their characteristic spectral features are naturally captured by a chiral pairing scenario. Our results establish a direct real-space connection between the superconducting gap and surface-extended quasiparticle states in PtBi${}_2$, and provide new insight into the nature of its unconventional surface superconductivity. These findings highlight PtBi${}_2$ as a versatile platform for exploring exotic quasiparticle excitations and potential Majorana physics.

arXiv commentRevised version with an updated title, author list, text, and figures. Supplementary Information has been added. The manuscript consists of 16 pages and 5 figures, with 7 additional figures in the extended data section