Quantum fluctuations and the ground-state phase diagram of the strong-coupling Holstein-Hubbard model
Institut für Theoretische Physik,
Philosophenweg 19, 69120 Heidelberg,
Accepted: 3 July 1997
A Grassmann functional integration technique is applied to the anisotropic pseudo spin Hamiltonian derived from the Holstein-Hubbard model with strong electron-phonon coupling. It is found that in those regions of the low-temperature phase diagram where superconductivity and the charge-density wave coexist already the static and homogeneous saddle point solution of the resulting field theory yields a ground-state energy which is lower than the classical result corresponding to the usual mean-field solution. This is due to the presence of quantum fluctuations and leads to new ground-state phase boundaries quantitatively different from those obtained in previous work by conventional operator decoupling schemes.
PACS: 71.27.+a – Strongly correlated electron systems; heavy fermions / 71.38.+i – Polarons and electron-phonon interactions / 75.10.Jm – Quantized spin models
© EDP Sciences, 1997