Robust Signatures of Fragile Topology in Nonmagnetic Materials
The paper introduces a fragile topological index Q to detect bulk Dirac cones in two-dimensional nonmagnetic materials with time-reversal and twofold rotation symmetry. This index is derived from relating Wilson and Euler loops, providing a robust spectroscopic signature that can be measured experimentally via ARPES or used in automated simulations. Verification on five real materials suggests its widespread applicability.