Fig. 2: Experimental Lorentz TEM images and diagram of observable states in a thin FeGe sample.

a–f, Representative over-focused Lorentz TEM images in a square 1 μm × 1 μm FeGe sample with a nominal thickness of 70 nm recorded at T = 95 K. a is a representative example of a ground state with helical spirals. b–f are representative images arranged in the order of increasing magnitude of external magnetic field, demonstrating the coexistence of skyrmions and antiskyrmions. b shows a stable skyrmion–antiskyrmion pair. A series of defocused Lorentz TEM images of this state is shown in Extended Data Fig. 5. c shows one skyrmionium, one skyrmion–antiskyrmion pair, two antiskyrmions at the lower edge and four skyrmions at the right edge. d shows two skyrmions and two antiskyrmions separated by a large distance. e shows five antiskyrmions and one skyrmion–antiskyrmion pair. f shows three antiskyrmions and two skyrmions. g, Temperature–field diagram of states observed with an increasing external magnetic field. The red and magenta squares indicate the collapse fields of skyrmions and antiskyrmions, respectively. The antiskyrmion collapse field is extrapolated towards T = 0 K based on micromagnetic estimations. The hatched region indicates the presence of helical spirals, which transform into surface modulations at higher fields, as shown in c, in the form of weak contrast features whose periodicity is larger than that of helical spiral L_D. The vertical dashed line at T_c = 287 K marks the Curie temperature of FeGe. T_a is the activation temperature, above which a skyrmion lattice spontaneously emerges in the red-shaded region (Supplementary Fig. 4). The symbols correspond to experimentally measured values, whereas the lines are guides to the eye. The error bars in our measurements are ~2 mT (0.1% of the objective lens current) and comparable with the size of the symbols.