Electron-hole Symmetry Breaking Research Articles

Superconductivity from electron-phonon interactions in the absence of electron-hole symmetry

Abstract We consider an electron-phonon Hamiltonian where the electron-phonon interaction occurs through a modification of both the electron on-site energy and the inter-site hopping amplitude, i.e. a combination of Holstein and Su-Schrieffer-Heeger (SSH)-like models. It is suggested that this model may apply to certain vibrational degrees of freedom in high T c oxides. This Hamiltonian is electron-hole asymmetric and reduces in the infinite-frequency limit to a model for hole superconductivity recently discussed. We solve the Eliasberg equations for the model and examine the effect of electron-hole symmetry breaking on T c in the presence of retardation.

Superconductivity from retarded interactions in the presence of electron-hole asymmetry.

We consider an electron-phonon Hamiltonian in which the electron-phonon interaction occurs through a modification of both the electron on-site energy and the intersite hopping amplitude, i.e., a combination of Holstein and Su-Schrieffer-Heeger (SSH)-like models. It is suggested that this model may apply to certain vibrational degrees of freedom in high-${\mathit{T}}_{\mathit{c}}$ oxides. This Hamiltonian is electron-hole asymmetric and reduces in the infinite-frequency limit to a model for hole superconductivity recently discussed. We solve the Eliashberg equations for the model and examine the effect of electron-hole symmetry breaking on superconductivity when the effective electron-electron interaction is retarded. It is found that superconductivity is enhanced by the electron-hole symmetry-breaking interaction even in the presence of strong retardation. Such an interaction is found to be more effective than an electron-hole symmetric interaction of equivalent magnitude in giving rise to superconductivity over a wide range of parameters for both high and low phonon frequencies. The carrier concentration dependence of the transition temperature in the electron-hole asymmetric model is found to become weaker as the phonon frequency decreases. Possible implications of our results for the understanding of superconductivity in real materials are discussed.

Note on the Electron-Hole Symmetry Breaking of the Energy Band Structure of Polyacetylene

SSH model is generalized to include the long-range hopping interactions to explain the electron-hole symmetry breaking of the energy band structure of polyacetylene.