Nonlinear ElectronLattice InteractionsTraditional treatments of the electronphonon interaction make two approximations: the lattice potential can be treated in the harmonic approximation and that the electronlattice interaction can be treated to linear order in the ion displacements. In the limit of strong coupling, however, these same models predict large lattice distortions, violating this assumption, and indicating the necessity of higherorder terms in the lattice displacement [1,2]. Examining nonlinear effects is, therefore, a necessary step towards fully understanding strong eph interactions. In two recent papers, we examined the effects of nonlinearity in the singleband Holstein model [3,4] and demonstrated that such interactions significantly alter the predictions of the linear model. This is illustrated in the figure above, which shows the CDW susceptibility for the halffilled Holstein model with linear and quadratic eph interactions. (The ratio of the quadratic and linear interaction strength is parameterized by ξ.) Here, the strong CDW correlations predicted by the linear model are suppressed by an order of magnitude when quadratic interactions of only 25% of the linear interaction strength are included. This is noteworthy because this ratio is typical of many models used to parameterize eph interactions in real materials. References

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