Effects of Cd vacancies and unconventional spin dynamics in the Dirac semimetal Cd3As2


Koumoulis D., Taylor R. E., McCormick J., Ertas Y. N., Pan L., Che X., ...More

JOURNAL OF CHEMICAL PHYSICS, vol.147, no.8, 2017 (SCI-Expanded) identifier identifier identifier

  • Publication Type: Article / Article
  • Volume: 147 Issue: 8
  • Publication Date: 2017
  • Doi Number: 10.1063/1.4999467
  • Journal Name: JOURNAL OF CHEMICAL PHYSICS
  • Journal Indexes: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Erciyes University Affiliated: No

Abstract

Cd3As2 is a Dirac semimetal that is a 3D analog of graphene. We investigated the local structure and nuclear-spin dynamics in Cd3As2 via Cd-113 NMR. The wideline spectrum of the static sample at 295K is asymmetric and its features are well described by a two-site model with the shielding parameters extracted via Herzfeld-Berger analysis of the magic-angle spinning spectrum. Surprisingly, the Cd-113 spin-lattice relaxation time (T-1) is extremely long (T-1 = 95 s at 295 K), in stark contrast to conductors and the effects of native defects upon semiconductors; but it is similar to that of C-13 in graphene (T-1 = 110 s). The temperature dependence of 1/T-1 revealed a complex bipartite mechanism that included a T-2 power-law behavior below 330 K and a thermally activated process above 330 K. In the high-temperature regime, the Arrhenius behavior is consistent with a field-dependent Cd atomic hopping relaxation process. At low temperatures, a T-2 behavior consistent with a spin-1/2 Raman-like process provides evidence of a time-dependent spin-rotation magnetic field caused by angular oscillations of internuclear vectors due to lattice vibrations. The observed mechanism does not conform to the conventional two-band model of semimetals, but is instead closer to a mechanism observed in high-Z element ionic solids with large magnetorotation constant [A.J. Vega et al., Phys. Rev. B 74, 214420 (2006)/. Published by AIP Publishing.