2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/160360We propose a many-body generalization of the Z2 topological invariant for the quantum spin Hall insulator, which does not rely on single-particle band structures. The invariant is derived as a topological obstruction that distinguishes topologically distinct many-body ground states on a torus. It is also expressed as a Wilson-loop of the SU(2) Berry gauge field, which is quantized due to the time-reversal symmetry.4 pages, 3 figures (final version to appear in Phys. Rev. Lett.)Mesoscale and Nanoscale Physicstext