Bulk Dirac Points in Distorted Spinels

Charles L. Kane, Eugene J. Mele and Andy M. Rappe (Seed)

The LRSM topological insulator (TI) seed is investigating how the connectivity of electronic bands in momentum space can be used to topologically classify insulators and semimetals. The theory of topological band structures has been generalized beyond TIs to include topological semimetals, including Weyl semimetals, Dirac semimetals and other symmetry protected topological states. 

The seed has focused on the three dimensional Dirac semimetal, a novel gapless material that is intermediate between a TI and an ordinary insulator.  This state has electronic structure similar to graphene but in all 3 dimensions, acting as though the excited carriers are massless. 

We have invented new materials that can offer these massless states, leading the way to new high-mobility electronics.


Designing a Dirac Semimetal:

  • Spinels with one B cation type (gray) form a 3D network of Bi, making hexagonal columns
  • We change the chemistry with B’ and B’’ ions
  • This breaks the hexagons and 3D network
  • Now have 1D chains and dimerized  Bi
  • Gives 3D linear dispersion, like graphene in 2D
  • Can enable new high-mobility electronic materials

Penn undergrad Julia Steinberg led this study in collaboration with LRSM TI Seed PIs. REU
PRL (in press) (2014)