Charge density waves and superconductivity in the electron-positive fermion gas using a simple intuitive model. Part II: Collective modes, effective interactions, superconductivity, and transport

Abstract

Superconductivity and the normal state electrical resistivity which varies as $T^2$ are strongly enhanced near the compressibility and charge density wave instabilities in the electron-positive fermion gas. The additional screening from the positive fermions introduces an attractive term in the effective electron-electron interaction that is the basis for superconductivity. Electron-positive fermion scattering is the source of the $T^2$ term in the electrical resistivity. At an instability, both interactions are divergent. The superconducting transition temperature is estimated using the McMillan formula. The electron-positive fermion gas conducts electricity and heat. Because electron-electron and positive fermion-positive fermion scattering conserve momentum, they do not contribute to the electrical resistivity, but electron-positive fermion scattering does. All three scattering mechanisms contribute to the thermal resistivity. The simple model for the electron-positive fermion gas is physically intuitive and naturally introduces instabilities at $q=0$ when the bulk modulus becomes zero and charge density waves at finite $q$ under some circumstances. For each mass ratio $M/m$, there is a unique density $r_s$ where the energy is a minimum. For different mass ratios, the interactions are investigated at several values of $r_s$ ranging from below the energy minimum to that of the instability.