Emergent Weyl fermion excitations in TaP explored by 181Ta quadrupole resonance
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The 181Ta quadrupole resonance [nuclear quadrupole resonance (NQR)] technique is utilized to investigate the microscopic magnetic properties of the Weyl semimetal TaP. We find three zero-field NQR signals associated with the transition between the quadrupole split levels for Ta with I=7/2 nuclear spin. A quadrupole coupling constant, νQ=19.250 MHz, and an asymmetric parameter of the electric field gradient, η=0.423, are extracted, in good agreement with band structure calculations. In order to examine the magnetic excitations, the temperature dependence of the spin-lattice relaxation rate (1/T1T) is measured for the f2 line (±5/2↔±3/2 transition). We find that there exist two regimes with quite different relaxation processes. Above T∗≈30 K, a pronounced (1/T1T) α T2 behavior is found, which is attributed to the magnetic excitations at the Weyl nodes with temperature-dependent orbital hyperfine coupling. Below T∗, the relaxation is mainly governed by a Korringa process with 1/T1T=const, accompanied by an additional T-1/2-type dependence to fit our experimental data. We show that Ta NQR is a novel probe for the bulk Weyl fermions and their excitations.
Yasuoka , H , Kubo , T , Kishimoto , Y , Kasinathan , D , Schmidt , M , Yan , B , Zhang , Y , Tou , H , Felser , C , Mackenzie , A P & Baenitz , M 2017 , ' Emergent Weyl fermion excitations in TaP explored by 181 Ta quadrupole resonance ' Physical Review Letters , vol 118 , no. 23 , 236403 . DOI: 10.1103/PhysRevLett.118.236403
Physical Review Letters
© 2017, American Physical Society. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at journals.aps.org / https://doi.org/10.1103/PhysRevLett.118.236403
T. K., Y. K., and H. T. appreciate the financial support from JSPS KAKENHI Grants (No. 15K21732 and No. 15H05885). D. K. acknowledges funding via FOR 1346 from the Deutsche Forschungsgemeinschaft.
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