Breaking of spatial inversion symmetry in anti-parallel-stacked ReSe₂

The development of mechanical exfoliation and dry-transfer techniques has made it possible to stack two-dimensional flakes dynamically and fabricate new materials that cannot be synthesized through thermodynamic processes. In such composite flakes, changes in the symmetry of the total system lead to a variety of emergent physical properties that would not appear in each component flake alone. Here, we fabricated an anti-parallel-stacked bilayer ReSe₂, which is expected to lose the spatial-inversion-symmetry by stacking the centrosymmetric monolayer flakes in the opposite directions. By micro-focused angle-resolved photoemission spectroscopy and second harmonic generation, we successfully observed the band dispersions and the artificially induced spatial inversion symmetry breaking in the anti-parallel-stacked bilayer ReSe₂. Our result demonstrates the potential for creating new materials that can exhibit spintronic functions and Berry-curvature-related physical phenomena by controlling the presence or absence of spatial inversion symmetry.