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Magnetic Doping of 3D Dirac Semimetals

Periodic Reporting for period 1 - MagDirac (Magnetic Doping of 3D Dirac Semimetals)

Reporting period: 2019-01-07 to 2021-01-06

After the discovery of 2D Dirac semimetals, the search for the 3D Dirac semimetal with a simple electronic structure continues. In topological Dirac semimetals, the bulk conduction and valence bands touch only at discrete (Dirac) points and disperse linearly along all three momentum directions, forming bulk (3D) Dirac fermions—a natural 3D counterpart of graphene. In addition to these bulk Dirac cones, some Dirac semimetals also possess topological non-trivial surface states, similar to those found in topological insulators. This unique electronic structure of topological Dirac semimetals gives rise to many unusual properties, such as the giant diamagnetism, giant linear magnetoresistance, oscillating quantum spin Hall effect and ultrahigh carrier mobility. In addition, an external magnetic field or magnetic doping in these materials can implement the breaking of the time-reversal symmetry, resulting Weyl semimetal phase. Therefore, here we proposed to investigate how the topological state (Dirac or Weyl) of semimetals can be tuned via its magnetic state. The overall objective of the project is to understand the interplay between magnetism and topological state of Dirac semimetals. This involves the growth of high quality single-crystalline thin films of 3D Dirac semimetals and controlling their magnetic state via magnetic doping.
During this reporting period, we made significant progress in the development of the MBE growth of α-Sn as a model 3D Dirac semimetal, as well as on magnetic doping of graphene as a 2D Dirac semimetal. We have grown pure, elemental and strained α-Sn films substrate using molecular beam epitaxy. The positive strain induced on α-Sn films leads to a topological insulator phase where topological Dirac cone from the surface states have been observed by angle-resolved photoemission spectroscopy (ARPES). Building on these results, we now aim to grow negatively strained thin films, as a model 3D Dirac semimetal.
The expected results at the end of the project will be (a) the realization of a pure stable elemental topological Dirac semimetal (α-Sn), (b) its controlled magnetic doping and (c) explore the Weyl semimetal phase induced by time-reversal symmetry breaking. These achievements constitute a crucial step towards the manipulation of topological Dirac semimetal phase via magnetic doping and pave the way for potential spintronic applications of Dirac semimetals.