## "Three-dimensional topological Dirac materials"
Although topologically nontrivial
properties are normally associated with insulating phases, recent developments
have shown that (semi)metallic phases can also be topological. In this talk, I
will survey recent developments regarding the topological classifications of
(semi)metallic materials in terms of crystal symmetries [1,2]. As a concrete
examples, I will present results about the recently discovered compound Ca3P2
[3], which has a line of Dirac nodes near the Fermi energy. I will discuss the
topological properties of Ca3P2 in terms of a low-energy effective theory and a
tight-binding model, derived from ab-initio DFT calculations. The microscopic
model for Ca3P2 shows that the drumhead surface states have a rather weak
dispersion, which implies that correlation effects are enhanced at the surface
of Ca3P2. Furthermore, I will discuss the parity anomaly that exists in this
nodal-line semimetal and show how it is connected to unusual transport
phenomena. As a second example, I will survey the topological properties of the
Dirac materials A3EO [4], where A denotes an alkaline earth metal, while E
stands for Pb or Sn. I will discuss the magnetic properties of this Dirac
system and show that a strong Zeeman field splits the gapped Dirac cones into
ungapped Weyl points, which are protected by a quantized Chern number. If time
permits, I will also present some results about non-centrosymmetric
superconductors and their Majorana flat-band surface states. |