Emergent Weyl Fermion Excitations in TaP Explored by ^{181}Ta Quadrupole Resonance

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Weyl semimetals are a novel class of topological materials with unique electronic properties.
• Understanding the microscopic magnetic properties of Weyl semimetals is crucial for exploring their potential applications.

Purpose of the Study:

• To investigate the microscopic magnetic properties of the Weyl semimetal tantalum phosphide (TaP).
• To explore the utility of the ^{181}Ta nuclear quadrupole resonance (NQR) technique for studying Weyl fermions.

Main Methods:

• Utilized the ^{181}Ta nuclear quadrupole resonance (NQR) technique.
• Measured the temperature dependence of the spin-lattice relaxation rate (1/T_{1}T) for specific NQR transitions.
• Analyzed NQR signals and relaxation rates to extract material parameters.

Main Results:

• Identified three zero-field NQR signals for Ta in TaP, yielding a quadrupole coupling constant ν_{Q}=19.250 MHz and asymmetry parameter η=0.423.
• Observed two distinct temperature regimes for spin-lattice relaxation, indicating different magnetic excitation processes.
• Found (1/T_{1}T)∝T^{2} behavior above T^{*}≈30 K, attributed to Weyl node excitations, and a Korringa process below T^{*}.

Conclusions:

• ^{181}Ta NQR is a powerful and novel probe for investigating bulk Weyl fermions and their magnetic excitations in TaP.
• The extracted NQR parameters agree well with theoretical band structure calculations.
• The temperature-dependent relaxation rates provide insights into the low-energy magnetic excitations near Weyl nodes.