The spin excitations from the nonmagnetic charge-ordered insulating state of α-(BEDT-TTF)2I3 at ambient pressure have been investigated by probing the static and low-frequency dynamic spin susceptibilities via site-selective nuclear magnetic resonance at C13 sites. The site-dependent values of the shift and the spin-lattice relaxation rate 1/T1 below the charge-ordering transition temperature (TCO≈135K) demonstrate a spin density imbalance in the unit cell, in accord with the charge-density ratio reported earlier. The shift and 1/T1 show activated temperature dependence with a static (shift) gap ΔS≈47-52meV and a dynamic (1/T1) gap ΔR≈40meV. The sizes of the gaps are well described in terms of a localized spin model, where spin-1/2 antiferromagnetic dimer chains are weakly coupled with each other.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics