  Weyl semimetals (WSMs) are topological quantum states wherein the electronic
bands linearly disperse around pairs of nodes, the Weyl points, of fixed (left
or right) chirality. The recent discovery of WSM materials triggered an
experimental search for the exotic quantum phenomenon known as the chiral
anomaly. Via the chiral anomaly nonorthogonal electric and magnetic fields
induce a chiral density imbalance that results in an unconventional negative
longitudinal magnetoresistance, the chiral magnetic effect. Recent theoretical
work suggests that this effect does not require well-defined Weyl nodes.
Experimentally however, it remains an open question to what extent it survives
when chirality is not well-defined, for example when the Fermi energy is far
away from the Weyl points. Here, we establish the detailed Fermi surface
topology of the recently identified WSM TaP via a combination of angle-resolved
quantum oscillation spectra and band structure calculations. The Fermi surface
forms spin-polarized banana-shaped electron and hole pockets attached to pairs
of Weyl points. Although the chiral anomaly is therefore ill-defined, we
observe a large negative magnetoresistance (NMR) appearing for collinear
magnetic and electric fields as observed in other WSMs. In addition, we show
experimental signatures indicating that such longitudinal magnetoresistance
measurements can be affected by an inhomogeneous current distribution inside
the sample in a magnetic field. Our results provide a clear framework how to
detect the chiral magnetic effect.
