Discovery of Helical Inorganic Crystals as Building Blocks for Chiral and Non-reciprocal Excitations

The realization of chiral and non-reciprocal excitations in inorganic crystalline materials necessitates the development of new atomically-precise chiral solid state crystals and understand their fundamental optical/electronic states that arise from the resulting structures. 

• Developed the chemistry to synthesize single crystals of a new 1D van der Waals helical crystal, GaSI, belonging to the deep class of III-VI-VII tetrahelices
• From first principles calculations and single crystal X-ray diffraction, we observed a stable, non-natural helical cross section in GaSI chains which manifests as a “squircle” geometry (hybrid between a square and a circle), imparting an oscillating curvature and torsion along the chain
• The 3.7 eV band gap GaSI packs in a newly observed non-centrosymmetric primitive unit cell (P-4) which led to the observation of pronounced second harmonic generation (SHG)