Fig. 1.

Alignment of the active nematic with a magnetic field. (A) Fluorescence micrograph of the active nematic with a pair of complementary +1/2 (blue) and −1/2 (red) defects highlighted. (B–H) Fluorescence micrographs with different configurations of the active nematic in the presence of a 4-kG uniform magnetic field. (B) The active fluid is initially in contact with nematic 8CB, which is transited, below T₀ = 33.4 °C, into the lamellar smectic-A phase (C) under a horizontal magnetic field. (D) The active nematic aligns perpendicularly to the field. By temperature cycling above (E and F) and below (G and H) T₀ under a vertical magnetic field, the active nematic is now realigned in the orthogonal direction (H). Pairs of aligned defects are highlighted in D and H. (I) Polarizing optical micrograph, and configuration of the underlying molecular planes in the SmA phase of the passive liquid crystal. (J) Fluorescence confocal micrograph revealing the correlation between the aligned active nematic and the anisotropic SmA phase. (K) Time average of the dynamic pattern. The arrows depict the antiparallel flow directions along the lanes of defect cores. (Scale bars: 100 μm.)