Comparative ${}^{181}$Ta-NQR Study of Weyl Monopnictides TaAs and TaP: Relevance of Weyl Fermion Excitations

Abstract

Based on our first detailed ${}^{181}$Ta nuclear quadrupole resonance (NQR) studies from 2017 on the Weyl semimetal TaP, we now extended our NQR studies to another Ta-based monopnictide TaAs. In the present work, we have determined the temperature-dependent ${}^{181}$Ta-NQR spectra, the spin-lattice relaxation time $T_1$, and the spin-spin relaxation time $T_2$. We found the following characteristic features that showed great contrast to what was found in TaP: (1) The quadrupole coupling constant and asymmetry parameter of EFG, extracted from three NQR frequencies, have a strong temperature dependence above $\sim$80 K that cannot be explained by the density functional theory calculation incorporating the thermal expansion of the lattice. (2) The temperature dependence of the spin-lattice relaxation rate, $1/T_{1}T$, shows a $T^4$ power law behavior above $\sim$30 K. This is a great contrast with the $1/T_{1}T\propto T^2$ behavior found in TaP, which was ascribed to the magnetic excitations at the Weyl nodes with a temperature-dependent orbital hyperfine coupling. (3) Regarding the nuclear spin-spin interaction, we found the spin-echo signal decays with the pulse separation simply by a Lorentzian function in TaAs, but we have observed spin-echo modulations in TaP that is most likely due to the indirect nuclear spin-spin coupling via virtually excited Weyl fermions. From our experimental findings, we conclude that the present NQR results do not show dominant contributions from Weyl fermion excitations in TaAs.

arXiv comment8 pages, 10 figures

References in corpus (16)

• Electronic Structure of Pyrochlore Iridates: From Topological Dirac Metal to Mott Insulator
• Wannier90: A Tool for Obtaining Maximally-Localised Wannier Functions
• Theoretical Discovery/Prediction: Weyl Semimetal states in the TaAs material (TaAs, NbAs, NbP, TaP) class
• Observation of the chiral anomaly induced negative magneto-resistance in 3D Weyl semi-metal TaAs
• Negative magnetoresistance without well-defined chirality in the Weyl semimetal TaP
• Extremely large magnetoresistance and ultrahigh mobility in the topological Weyl semimetal NbP
• Topological response in Weyl semimetals and the chiral anomaly
• Signatures of the Adler-Bell-Jackiw chiral anomaly in a Weyl Fermion semimetal
• Optical Signatures of Weyl Points in TaAs
• Chiral Quasiparticles at the Fermi Surface of the Weyl Semimetal TaAs
• Interplay between localized and itinerant magnetism in Co substituted FeGa${}_3$
• Emergent Weyl fermion excitations in TaP explored by 181-Ta quadrupole resonance
• Anomalous hyperfine coupling and nuclear magnetic relaxation in Weyl semimetals
• Exotic Landau Diamagnetism and Weyl-Fermions Excitations in TaAs Revealed by ${}^{75}$As NMR and NQR
• Nuclear spin-lattice relaxation time in TaP and the Knight shift of Weyl semimetals
• ${}^{239}$Pu nuclear magnetic resonance in the candidate topological insulator PuB${}_4$

Cited by in corpus (1)

• Experimental nuclear quadrupole resonance and computational study of the structurally refined topological semimetal TaSb${}_2$