Topological nodal $i$-wave superconductivity in PtBi$_2$

TL;DR

This paper reports the discovery of topological $i$-wave superconductivity in PtBi$_2$, featuring nodes in the superconducting gap and topologically protected Majorana states, advancing the understanding of unconventional superconductors.

Contribution

It provides experimental evidence of $i$-wave pairing and topological Majorana states in PtBi$_2$, a Weyl semimetal, highlighting its potential for quantum computing applications.

Findings

Observation of nodes in the superconducting gap at Fermi arcs

Gapping of topological surface states below 10 K

Prediction of Majorana flat bands at surface step edges

Abstract

Most superconducting materials are well-understood and conventional in the sense that the pairs of electrons that cause the superconductivity by their condensation have the highest possible symmetry. Famous exceptions are the enigmatic high-$T_c$ cuprate superconductors. Nodes in their superconducting gap are the fingerprint of their unconventional character and imply superconducting pairing of $d$-wave symmetry. Here, using angle-resolved photoemission spectroscopy, we observe that the Weyl semimetal PtBi$_2$ harbors nodes in its superconducting gap, implying unconventional $i$-wave pairing symmetry. At temperatures below $10\,\mathrm{K}$, the superconductivity in PtBi$_2$ gaps out its topological surface states, the Fermi arcs, while its bulk states remain normal. The nodes in the superconducting gap that we observe are located exactly at the center of the Fermi arcs, and imply the presence of topologically protected Majorana cones around this locus in momentum space. From this, we infer theoretically that robust zero-energy Majorana flat bands emerge at surface step edges. This not only establishes PtBi$_2$ surfaces as unconventional, topological $i$-wave superconductors but also as a promising material platform in the ongoing effort to generate and manipulate Majorana bound states.