Seeking definitive experimental signatures of a Weyl semimetal

Weyl and Dirac semimetals are getting quite a bit of attention. Part of this interest is because of the possible solid state realisation of the chiral anomaly from quantum field theory. One proposed signature is negative longitudinal magnetoresistance. A different, arguably more definitive, signature is in the following paper.

Quantum oscillations from surface Fermi arcs in Weyl and Dirac semimetals 
Andrew C. Potter, Itamar Kimchi, and Ashvin Vishwanath

In a thin slab of material there are "Fermi arc" states on the top and bottom surfaces. When a magnetic field is applied perpendicular to the slab, there are unusual closed orbits (shown below) where an electron can move around the arc on the  top surface, tunnel via a bulk chiral state to the bottom surface, move around the arc on the bottom surface, and then tunnel back to the top surface.

The resulting Shubnikov de Haas oscillations have some unique signatures such as the periodicity and the dependence of the phase of the oscillations on the thickness of the sample.

There is a very nice set of experiments to test these ideas.

Chirality transfer dynamics in quantum orbits in the Dirac semi-metal Cd3As2 
Philip J.W. Moll, Nityan L. Nair, Tony Helm, Andrew C. Potter, Itamar Kimchi, Ashvin Vishwanath, James G. Analytis

The main finding of this study is directly evident in the raw data: while parallel [magnetic] fields lead to a single SdH frequency , an additional higher frequency component Fermi surface associated with the surface oscillations appears for fields perpendicular to the surface. This high frequency is clearly distinguishable from higher harmonics of the low frequency Fermi surface.

Focused Ion Beams were used to prepare samples with different geometries, rectangular and triangular, shown below. In the latter the oscillations associated with chirality are washed out by destructive interference due to the dependence of phase on the slab thickness.

Aside: In Figure 3 they show experimental signatures of hydrodynamic flow.

I thank James Analytis for helpful discussions about this work.

There is a also very nice theory paper.
Axial anomaly and longitudinal magnetoresistance of a generic three dimensional metal 
 Pallab Goswami, J. H. Pixley, S. Das Sarma

It is quite pedagogical, comprehensive in scope, and contains some important new insights. One particularly significant one is that one can get negative magnetoresistance without a Weyl or Dirac metal. Furthermore, in a system with a cylindrical Fermi surface, near the Yamaji angles [normally associated with semi-classical Angle Dependent Magnetoresistance Oscillations (AMRO)] one can have only one partially full Landau level, leading to negative longitudinal magnetoresistance.

Hopefully once I have digested this paper  more I will write something. I am particularly curious as to whether this theory can explain the unusual angle-dependent interlayer magnetoresistance seen in a diverse set of strongly correlated electron metals.