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Long-range charge order in the extended Holstein--Hubbard model

This study investigated the extended Holstein--Hubbard model at half-filling as a model for describing interplay of the electron-electron and electron-phonon couplings. When the electron-phonon and nearest-neighbor electron-electron interactions are strong, we prove the existence of long-range charge order at sufficiently low temperature in three or more dimensions. As a result, we rigorously justify the phase competition between the antiferromagnetic and charge orders.