1 research outputs found
Band Ordering and Dynamics of Cu<sub>2–<i>x</i></sub>Te and Cu<sub>1.98</sub>Ag<sub>0.2</sub>Te
<sup>63</sup>Cu, <sup>65</sup>Cu, and <sup>125</sup>Te NMR measurements
are reported for Cu<sub>2–<i>x</i></sub>Te and Cu<sub>1.98</sub>Ag<sub>0.2</sub>Te. The results demonstrate an onset of
Cu-ion hopping below room temperature, including an activation behavior
consistent with high-temperature transport measurements but with a
significant enhancement of the hopping barriers with Ag substitution.
We also separated the Korringa behavior by combining NMR line shape
and relaxation measurements, thereby identifying large negative chemical
shifts for both nuclei, as well as large Cu and Te s-state contributions
in the valence band. Further comparison was obtained through heat
capacity measurements and chemical shifts computed by density functional
methods. The large diamagnetic chemical shifts coincide with behavior
previously identified for materials with topologically nontrivial
band inversion, and in addition, the large metallic shifts point to
analogous features in the valence band density of states, suggesting
that Cu<sub>2</sub>Te may have similar inverted features