Spontaneous ferromagnetism in magic angle twisted bilayer MoTe₂

The recent realization of the fractional quantum anomalous Hall effect (FQAHE) in a twisted MoTe₂ bilayer (tMoTe₂) establishes a powerful platform for researching topological quantum many-body physics. A unique feature of the system is the existence of a wide range of twist angles (over 2^o) that achieve a narrow bandwidth in the first Chern band, and thus FQAHE. However, for the second Chern band, theory suggests that the bandwidth varies rapidly but reaches a minimum near a magic angle of around 2.1^o. It is predicted that exotic states may be realized by filling the second Chern band at this magic angle. Here, I present robust spontaneous ferromagnetism and thus broken time reversal symmetry at v = -3 for 2.1^o tMoTe₂. The observed ferromagnetic state is electrically tunable and covers a broad doping range near v= -3. In addition, we observe the ferromagnetism near v = -1 that continuously extends over v = -1.5, satisfying a prerequisite for engineering a 3/2 fractional Chern insulator state. Our results pave the way for engineering exotic correlated topological states in fractional Chern insulators.