Theoretical calculation of the wave vector and frequency dependent dielectric function for YBa2 Cu3 O7

If the dielectric function of a material is negative in some region of ω, q space, an attractive interaction between electrons may result. An attractive interaction may lead to superconductivity. The authors have calculated the dielectric function of YBa2 Cu3 O7 as functions of ω and q in the random phase approximation, using a parameterized tight binding band structure. Only the contribution from electronic interband transitions is considered. They find resonance structure in the dielectric function for energies above 0.2 eV, including regions where the real part is negative. Detailed results and implications are discussed