Static and Dynamic Electronic Properties of Weyl Semimetal NbP - A Single Crystal 93Nb-NMR Study

Nuclear magnetic resonance (NMR) techniques have been used to study the static and dynamic microscopic properties of the Weyl semimetal NbP. From a complete analysis of the angular dependence of the Nb-93-NMR spectra in a single crystal, the parameters for the electric quadrupole interactions and the magnetic hyperfine interactions were determined to be nu(Q) = 0.61 MHz, eta = 0.20, (K-XX, K-YY, K-ZZ)=(-0.06,0.11,-0.11)% at 4.5 K. The temperature and field dependence of the Nb-93 Knight shift revealed a characteristic feature of the shape of the density of states with nearly massless fermions. We clearly observed a quantum oscillation of the Knight shift associated with the band structure, whose frequency was in good agreement with the previous bulk measurements. The temperature dependence of the spin-lattice relaxation rate, 1/T1T, showed an almost constant behavior for 30 < T < 180 K, while a weak temperature dependence was observed below similar to 30 K. This contrasts with the behavior observed in TaP and TaAs, where the 1/T1T measured by the Ta-181 nuclear quadrupole resonance (NQR) shows 1/T1T proportional to T-2 and T-4 above approximately 30 K. In TaP, the temperature dependent orbital hyperfine interaction plays a significant role in nuclear relaxation, whereas this contribution is not observed in TaAs. Two-component spin echo oscillations were observed. The shorter-period oscillation is attributed to the origin of quadrupole coupling, while the longer-period oscillation indicates the presence of indirect nuclear spin-spin coupling, as discussed in other Weyl semimetal like TaP.