Speaker
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Trigonal PtBi₂ has emerged as a compelling platform for studying the interplay between crystal symmetry, topology, and superconductivity [1,2,3]. In this noncentrosymmetric Weyl semimetal, the absence of inversion symmetry and strong spin–orbit coupling give rise to topological surface states, while superconducting signatures appear to be strongly inhomogeneous from the nano- to the microscale and, remarkably, confined to the surface Fermi arcs [4,5]. This unusual behavior suggests that the superconducting properties of PtBi₂ may be intimately linked not only to its electronic topology, but also to subtle structural distortions and local symmetry breaking within its layered lattice. Understanding how these local structural degrees of freedom evolve is therefore essential for clarifying the origin of its unconventional superconducting response.
This complex scenario requires a combined approach capable of disentangling the structural and electronic ingredients that contribute to the unique behavior of PtBi₂. In this work, we use temperature-dependent X-ray absorption spectroscopy (XAS) and submicron spatially resolved angle-resolved photoemission spectroscopy (nanoARPES) to correlate local structural distortions with the surface electronic properties. The XAS results reveal an anomalous temperature evolution of the local atomic environment, characterized by two distinct upturns around 200 K and 60 K, possibly indicating the onset of competing or intertwined ordering tendencies that shape the low-temperature properties of PtBi₂. Notably, recent scanning tunneling spectroscopy and second harmonic generation studies have suggested that the anomaly near 60 K may be connected to real onset of surface superconductivity, whose spectroscopic signatures are otherwise detected at much lower temperatures [6,7]. Complementary nanoARPES measurements further reveal spatial fluctuations of the surface electronic states that correlate with local variations of the Bi-terminated surface, with a distinct change in the electronic response across the 60 K anomaly. These results point to a close connection between local lattice distortions, surface electronic inhomogeneity, and the unconventional superconducting phenomenology of trigonal PtBi₂.
References:
[1] K Takaki et al. (2022). Journal of the Physical Society of Japan, 91(3), 034703.
[2] A. Kuibarov et al. (2024). Nature, 626(7998), 294-299
[3] S. Changdar et al.. (2025).. Nature, 647(8090), 613-618.
[4] S. Palumbo et al. (2025). Phys. Rev. B, 112(20), 205125
[5] S. Schimmel et al. (2024). Nature Communications, 15(1), 9895
[6] B. Chavez et al. (2023). Physical Review B, 108(22), 224104
[7] J. Besproswanny et al. (2025). arXiv preprint arXiv:2507.10187.