Microscopic origin of gray tracks in <mml:math xmlns:mml="http://www..org/1998/Math/MathML"><mml:msub><mml:mi>KTiOPO</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:math>
A. Bocchini, U. Gerstmann, W.G. Schmidt, Physical Review B 111 (2025).