The discoveries of quantum Hall effect and topological insulators broaden the understanding of fundamental states of quantum matter. In topological view, the quantum matter can be divided into topological trivial and non-trivial materials. The three-dimensional (3D) topological Dirac semimetal is a new type of topologically non-trivial materials, in which the conduction and valence band touch only at discrete points and disperse linearly along all (three) momentum directions—a natural 3D counterpart of graphene, as well as a gapless topological semimetal. More interestingly, the 3D Dirac semimetal is on the boundary of various topological materials. It means that by modulation, the 3D Dirac semimetal can be driven into other topological states, such as Weyl semimetal, topological insulator and even topological superconductors. In particular, topological superconductors are superconducting in bulk state but support gapless Majorana fermions in the boundary. In solid state physics, Majorana fermions are new quasiparticles from the theoretical point of view, and it is shown that Majorana zero modes can be applied for topological quantum computation. Thus, topological superconductivity is of great importance in both fundamental science and potential applications. However, so far the experimental demonstrations are still under debate.

Recently, Prof. Jian Wang etc, based on previous transport studies on 3D Dirac semimetal Cd3As2(Physical Review X 5, 031037(2015)), in collaboration with Prof. Jian Wei, Prof. Xiong-Jun Liu, Prof. X. C. Xie and Prof. Shuang Jia at Peking University, discovered superconductivity induced by hard point contact on 3D Dirac semimetal Cd3As2 crystals. The point contact spectroscopy measurement reveals the characteristics of unconventional superconductivity. Furthermore, the zero bias conductance peak is observed, which might originate from Majorana fermions. This work indicates that the 3D Dirac semimetal could be modulated to potential topological superconductor in the contact region by hard point tip or probe. More importantly, the results reveal a new way to detect and study topological superconductivity by using hard tip/point contact on topological non-trivial materials, which is different with the prevailing proximity effect method for creating topological superconductivity or Majorana fermions.

The paper was online published in Nature Materials on November 2, 2015 (Nature Materials (2015) doi:10.1038/nmat4456): http://www.nature.com/nmat/journal/vaop/ncurrent/full/nmat4456.html. Prof. Jian Wang, Prof. Jian Wei and Prof. Xiong-Jun Liu are corresponding authors of this paper. He Wang, Huichao Wang and Dr. Haiwen Liu contributed equally to this work.

The work was supported by National Basic Research Programs of China, National Natural Science Foundation of China, 1000 Talents Program for Young Scientists of China, the Research Fund for the Doctoral Program of Higher Education (RFDP) of China, and Collaborative Innovation Center of Quantum Matter, China.