Nonlinear electric transport and switching phenomenon in the mixed-stack charge-transfer crystal tetrathiafulvalene-p-chloranil

A remarkable nonlinearity and a switching effect have been observed for electric transport in a tetrathiafulvalene (TTF)-$p$-chloranil crystal. Experimental evidence indicates that these features are of an intrinsic origin associated with the neutral-ionic transition. A possible mechanism is discussed in terms of field-dependent low-energy excitations, such as solitons and neutral-ionic domain walls, which are inherent to the quasi-one-dimensional donor-acceptor stacks in the TTF-$p$-chloranil crystal.