Chiral anomaly in doped <b> <i>α</i> </b>-Sn films by Fermi level tuning

Gray tin (α-Sn) is an elemental topological material with various topological phases. It is predicted to be a 3D Dirac semimetal when appropriate strain is applied. However, the Dirac semi-metallic properties, such as chiral anomaly, are hard to be observed, probably due to the imperfections in the α-Sn samples. It is even more challenging to manipulate the topological properties in this metastable material without a sacrifice in the crystalline quality. Here, we report a strategy of Fermi level tuning by doping the α-Sn films grown on CdTe (001) substrates by molecular beam epitaxy. The negative magnetoresistance and planar Hall effect, which are attributed to chiral anomaly, are observed in α-Sn when the Fermi level is tuned close to the bulk Dirac point. Detailed analyses of Shubnikov–de Haas oscillations show nontrivial Berry phases for all the samples. Combined with first-principle calculations, these results provide a strong evidence of the three-dimensional Dirac semimetal phase in α-Sn. Furthermore, a clear transition from two-dimensional topological surface states to three-dimensional bulk Dirac cone is demonstrated in α-Sn by precise Fermi level tuning through doping. This study proves the 3D Dirac semimetal phase in α-Sn and provides an effective strategy to manipulate the topological properties for both fundamental studies and device applications.