Robust continuous time crystal in an electron–nuclear spin system

Crystals spontaneously break the continuous translation symmetry of free space. Analogously, time crystals lift translational invariance in time. Here we demonstrate a robust continuous time crystal in an electron–nuclear spin system of a semiconductor tailored by tuning the material composition. Continuous, time-independent external driving of the sample produces periodic auto-oscillations with a coherence time exceeding hours. Varying the experimental parameters reveals wide ranges in which the time crystal remains stable. At the edges of these ranges, we find chaotic behaviour with a lifted periodicity corresponding to the melting of the crystal. The time crystal state enables fundamental studies of nonlinear interactions and has potential applications as a precise on-chip frequency standard.