Experimental nuclear quadrupole resonance and computational study of the structurally refined topological semimetal TaSb_2
arxiv(2023)
摘要
The local electric field gradients and magnetic dynamics of TaSb_2 have
been studied using ^121Sb, ^123Sb, and ^181Ta nuclear quadrupole
resonance (NQR) with density functional theory (DFT) calculations using
XRD-determined crystal structures. By measuring all structurally expected
thirteen NQR lines, the nuclear quadrupole coupling constant (ν_Q) and
asymmetric parameter (η) for Ta, Sb(1), and Sb(2) sites were obtained.
These values are all in good agreement with the presented DFT calculations.
Principal axes of the electric field gradients was determined for a
single-crystal sample by measuring the angular dependencies of NMR frequency
under a weak magnetic field. The unusual temperature dependence of η(T) of
Sb(2) hints at the suppressed thermal expansion along the a-axis. Spin
lattice relaxation rate (1/T_1T) measurements reveal an activated-type
behavior and an upturn below 30 K. Neither the low temperature upturn nor the
high temperature activation type behaviors are reproduced by the calculated
1/T_1T based on the calculated density of states (DOS). On the other hand,
the agreement between the calculated DOS and specific heat measurements
indicates that the band renormalization is small. This fact indicates that
TaSb_2 deviates from the simple semimetal scenario, and magnetic excitations
are not captured by Fermi liquid theory.
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