Giant enhancement of anisotropy by electron-phonon interaction

Anisotropic electron-phonon interaction is shown to lead to the anisotropic polaron effect. The resulting anisotropy of the polaron band is an exponential function of the electron-phonon coupling and might be as large as ${10}^{3}$. This also makes anisotropy very sensitive to small changes of coupling and implies wide variations of anisotropy among compounds of similar structure. The isotope effect on mass anisotropy is predicted. Polaron masses are obtained by an exact quantum Monte Carlo method. Implications for high-temperature superconductors are briefly discussed.

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