Fig. 1: Coalescence of two nuclei with parallel triangle lattices and incoherent triangle-square interfaces.

The colours in (a–f) represent the dynamic Lindemann parameter for each particle measured within 4 s (Methods). Heating light is switched on at t = 0. Scale bar: 5 μm. a At 1040 s, one nucleus forms. b Another nucleus forms at 1060 s. The yellow solid lines indicate the closest facets of the two nuclei. The misorientation angle is β₁ = 45^∘, between the [10] directions of the square and triangle lattices. The dashed line shows the interface position of the left nucleus at 1040 s, and r_left measures the distance that the interface moves. c The growth of the two nuclei distort the square lattice between them. α is defined as the angle between the [10] direction of square-lattice and x-axis of the lab frame. The white hollow stars mark two interstitials generated by the lattice distortion. d, e The two nuclei coalesce at 1155 s by forming a thin channel of triangle lattice. f The fully coalesced nucleus contains a dislocation (⊥) owing to the slight mismatch of the orientations of the two triangle lattices. g The displacements r of the two nuclei’s facets with respect to their initial positions (yellow lines in (a, b)) and their separation d. The green and red regions represent the stages that nuclei grow faster and merge together, respectively. h The evolution of the four-fold orientational order parameter, ∣ψ₄∣, and the [01] direction α of the square-lattice in the yellow rectangle region in (c). The blue, green and red lines in (g) and (h) indicate the evolution trend of parameters in various stages.