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The next generation of Dirac materials, from discovery to new physical phenomena realized in the solid state

Einladung zum Physikalischen Kolloquium im Wintersemester 2016/17

In this talk I will discuss the recent progress of research in the field of Dirac materials. I will discuss the challenges this field is still facing and introduce a materials chemist’s view on identifying new candidate materials.

3D Dirac materials (3D DMs) are materials that have the same electronic structure as graphene, i.e. they host mass-less electrons that behave like photons rather than usual electrons. They can be identified from their electronic structure that features linearly dispersed bands that cross at a single point, called a Dirac point. Recently, there has been considerable interest in these materials because they exhibit exotic physical properties such as ultra-high mobilities, as well as very large magnetoresistance (MR). These make 3D DMs promising for different applications, for example in electronics or data storage. Additionally, the high carrier mobility could be useful for other devices such as thermoelectrics or transport layers in solar cells.

Furthermore, 3D DMs are of interest for fundamental physics. The discovery of the Weyl fermion in Dirac materials with broken inversion symmetry last year was a milestone for particle physics realized in a solid material.

In order to use 3D DMs for any kind of applications, new better materials are required. I will introduce the first stable, cheap and non-toxic 3D DSM, which is currently the best candidate material for future applications.

Further, compounds that crystallize in non-symmorphic space groups recently gained a lot of attention from theoretical physicsts. In space groups that are non-symmorphic, the glide planes or screw axis cause a doubling of the unit cell. This leads to a folding BZ and causes the bands to be degenerate at the BZ boundaries and can thus yield Dirac cones. A very recent prediction suggested that non-symmoprhic symmetry can also lead to types of fermions that are distinct form Dirac, Weyl or Majorana. These exotic new quasiparticles have yet to be discovered.

Problematic for realizing this types of Dirac materials is that they require and odd band filling in order to have the Fermi level located at or near the band crossing points. I will explain why it is chemically very challenging to realize that and point to some solutions which could lead to the discovery of the proposed new quasiparticles

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