Topological superconductivity in hourglass Dirac chain metals (Ti, Hf)IrGe

TL;DR

This paper reports the discovery of topological superconductivity candidates in TiIrGe and HfIrGe, featuring hourglass Dirac chains, topological surface states, and conventional bulk superconductivity, providing promising platforms for quantum technology applications.

Contribution

It introduces new ternary germanide superconductors with nonsymmorphic symmetry-protected topological features and demonstrates their potential for topological superconductivity.

Findings

TiIrGe and HfIrGe are bulk type-II superconductors with full gaps.

These materials exhibit hourglass Dirac chains and topological surface states.

Nontrivial $ ext{Z}_2$ topology supports helical spin textures near the Fermi level.

Abstract

Realizing topological superconductivity in stoichiometric materials is a key challenge in condensed matter physics. Here, we report the discovery of ternary germanide superconductors, $M$IrGe ($M$ = Ti, Hf), as prime candidates for topological superconductivity, predicted to exhibit nonsymmorphic symmetry-protected hourglass Dirac chains. Using comprehensive thermodynamic and muon-spin rotation/relaxation ($\mu$SR) measurements, we establish these materials as conventional bulk type-II superconductors with transition temperatures of 2.24(5) K for TiIrGe and 5.64(4) K for HfIrGe, featuring a full gap and preserved time-reversal symmetry. First-principles calculations reveal striking topological features in $M$IrGe, including hourglass-shaped bulk dispersions and a Dirac chain -- a ring of fourfold-degenerate Dirac points protected by nonsymmorphic symmetry. Each Dirac point corresponds to the neck of the hourglass dispersion, while the Dirac chain gives rise to drumhead-like surface states near the Fermi level. Additionally, nontrivial $\mathbb{Z}_2$ topology leads to isolated Dirac surface states with helical spin textures that disperse across the Fermi level, forming an ideal platform for proximity-induced topological superconductivity. The coexistence of conventional bulk superconductivity, symmetry-protected hourglass topology, and helical spin-textured surface states establishes $M$IrGe as a rare and robust platform to realize topological superconductivity, opening new avenues for next-generation quantum technologies.