Coincident site lattice concept

However, the experimental results do not allow one to decide whether the rotation of the Pb UPD overlayer (cf. eq. (3.22)) can be explained by the coincident site lattice" concept (involving higher order commensurate overlayers, Fig. 3.17) or the static distortion waves" (SDW) concept (dealing with incommensurate overlayers, Fig. 3.18). The estimation of d as a function of AE from a statistical analysis of in situ STM images coincides with GKS results illustrated in Fig. 3.27 [3.176]. 

Most theories of structural superlubricity are based on the Prandtl-Tomlinson model or the more advanced Frenkel-Kontorova model [1043, 1044], in which the single atom/tip is replaced by a chain of atoms coupled by springs. However, Friedel and de Gennes [1045] noted recently that correct description of relative sliding of crystalline surfaces should include the motion and interaction of dislocations at the surfaces. This concept was taken up by Merkle and Marks [1045] and generalized using the well-established coincident site lattice theory and dislocation drag from solid-state physics. 

More recently, D. Emin [24] developed an alternative analysis of activated hopping by introducing the concept of coincidence. The tunneling of an electron from one site to the next occurs when the energy state of the second site coincides with that of the first one. Such a coincidence is insured by the thermal deformations of the lattice. By comparing the lifetime of such a coincidence and the electron transit time, one can identify two classes of hopping processes. If the coincidence lime is much laigcr than the transit lime, the jump is adiabatic the electron has lime to follow the lattice deformations. In the reverse case, the jump is non-adia-batic. 

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