Butterfly Magnetoresistance, Quasi-2D Dirac Fermi Surfaces, and a   Topological Phase Transition in ZrSiS
  Magnetoresistance (MR), the change of a material's electrical resistance in response to an applied magnetic field, is a technologically important property that has been the topic of intense study for more than a quarter century. Here we report the observation of an unusual "butterfly" shaped titanic angular magnetoresistance (AMR) in the non-magnetic, Dirac material, ZrSiS. The MR is large and positive, reaching nearly 1.8 x 10^5 percent at 9 T and 2 K at an angle of 45o between the applied current (along the a-axis) and the applied field (90o is H parallel to the c-axis). Approaching 90o, a "dip" is seen in the AMR which can be traced to an angle dependent deviation from the H^2 law. By analyzing the SdH oscillations at different angles, we find that ZrSiS has a combination of 2D and 3D Dirac pockets comprising its Fermi surface and that the anomalous transport behavior coincides with a topological phase transition whose robust signature is evident despite transport contributions from other parts of the Fermi surface. We also find that as a function of angle, the temperature dependent resistivity in high field displays a broad peak-like behavior, unlike any known Dirac/Weyl material. The combination of very high mobility carriers and multiple Fermi surfaces in ZrSiS allow for large bulk property changes to occur as a function of angle between applied fields makes it a promising platform to study the physics stemming from the coexistence of 2D and 3D Dirac electrons. 
Mazhar N. Ali, Leslie M. Schoop, Chirag Garg, Judith M. Lippmann, Eric   Lara, Bettina Lotsch, Stuart Parkin
cond-mat.mtrl-sci