Figure 1

(a) Displacements of atoms’ equilibrium positions produce a potential well for a carrier (red dot) that localizes it at a site. (b) Amidst atoms’ vibrations a coincidence configuration is occasionally achieved. The carrier is then shared between sites (paired orange dots). Two coincident energy levels are split by twice the electronic transfer energy $t$. Carrier-induced softening occurs as the intersite motion of a charge carrier reduces the stiffness of the associated atomic vibrations. (c) A hop is completed when a carrier settles on another site as atoms’ vibration energy is dissipated to surrounding atoms. The thickness of the (blue) bars representing carrier energy levels indicates their variations due to thermal atomic vibrations.Reuse & Permissions