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  1. Significance

    The quasi–1-dimensional bismuth bromide, α-Bi4Br4, has been predicted to be a rotational symmetry-protected topological crystalline insulator. The structural study under high pressure indicates that the α-Bi4Br4phase is stable up to 4.3 GPa. There is a rich phase diagram of physical properties under high pressure in the α-Bi4Br4phase (i.e., a pressure-induced insulator–metal transition and, most importantly, a superconductive phase near the boundary of the insulator–metal transition). These findings help to answer questions, such as whether it is possible for the symmetry-protected electrons to form Cooper pairs. The α-Bi4Br4undergoes a pressure-induced structural transition above 4.3 GPa to a triclinicP-1 phase, which is another superconductive phase.

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