Coexistence of superconductivity and weak ferromagnetism at the interface of twisting bicrystals of 3D topological insulator Bi1 − xSbx (0.07 < x < 0.2)

In the normal state the 3D topological insulator Bi1 − xSbx is diamagnetic and does not show superconductivity because of the extremely low carrier density. Despite this, we have found that the small crystallite disorientation angle (SDA) interfaces of bismuth-antimony bicrystals, which consist of a solitary central part (thickness of about 60 nm) and two similar adjacent layers (∼20 nm) on both sides of it, exhibit two superconducting transitions with critical temperature Tc∼(3.7-4.6) K and Tc∼(8.3-21) K, while large crystallite disorientation angle (LDA) interfaces with a higher structural disorder show ferromagnetic hysteresis loops and specific characteristics of a single superconducting layer with a thickness comparable with the entire interface.