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Description
The organic charge transfer salt TTF-CA contains 1D chains with alternating molecules of the electron donor TTF and the electron acceptor chloranil (CA). At high temperatures the molecules are in a charge neutral state (N), but below 80 K there is an ionic state (I) with a partial charge transfer from TTF to CA. Various topological excitations are possible in this system [1], e.g. domain walls between N and I regions and spin or charge solitons at the boundaries between I regions with different order. In NMR the spin solitons are only observed for pressure above 7 kbar [2], however our $\mu$SR studies show that mobile spin solitons are also produced in TTF-CA under ambient pressure, with the help of muon addition to the molecules. The dependence of the muon relaxation rate on magnetic field B shows the B$^{-1/2}$ power law, consistent with 1D diffusion [3]. Information about the degree of charge transfer can also be obtained from studies of the time domain signal within a low-field avoided level crossing resonance associated with the CA molecule.
1. K. Sunami et al, ‘Topological Excitations in Neutral–Ionic Transition Systems’, Symmetry 14, 925 (2022).
2. K. Sunami et al, ‘Evidence for solitonic spin excitations from a charge-lattice-coupled ferroelectric order’, Sci Adv. 4, eaau7725 (2018).
3. Y. Sakai and C. Hotta, ‘Diffusive dynamics of fractionalised particles and the enhanced conductivity at the border of the neutral-ionic transition’, Phys. Rev. B 110, 174306 (2024).
| francis.pratt@stfc.ac.uk |
