Magnetic resonance as a local probe for linear bands in the Weyl semimetals NbP and TaP

Some compensated d-electron semimetals, for example the monophosphites NbP and TaP, with non centrosymmetric structure and with sizable spin orbit coupling (SOC) form a new class of material: the Weyl semimetals (WSM). A unique linear crossing of valence- and conduction- band in a single point in reciprocal space defines the so called Weyl point where the fermion mass vanishes theoretically. In real materials the Fermi level E_F does not exactly match the Weyl node and as a consequence residual very light fermions are found. Due to the SOC these Weyl fermions have a chirality (handedness) on their linear dispersive (E ∝k) bands and frequently a linear density of states (DOS) at the Fermi level E_F. We use NMR as a probe for this linear d- electron bands. The shift provides the s- and d- electron contributions to the DOS at E_F, whereas the spin lattice relaxation is governed by low energy excitations around E_F. ³¹P (I = 1/2) - Fourier - transform - and ⁹⁵Nb (I = 9/2) - broadline - sweep - NMR studies are performed. We investigated powder samples as well as single crystals on both systems. The angular dependence of the ⁹⁵Nb- and ³¹P - NMR lines is discussed.