Anomalous dispersion of surface impedance and negative dielectric permeability in Tl₂Ba₂Cu₃O₁₄

Aimed to study unusual high-frequency properties of high-temperature superconductors (HTSC) measurements of frequency dependences of real and imaginary parts of surface impedance of Tl₂Ba₂Ca₂Cu₃O₁₄ compound were carried out within 10-130 MHz and 2-6 GHz at room temperature. Anomalous dispersion of imaginary part of surface impedance within the frequency range of 150 MHz to 2 GHz was revealed. It was shown that at frequencies above 2 GHz a real part of dielectric permeability appeared which was comparable to its imaginary part in modulus and negative in sign. The investigations conducted were pointed out to give the information on the nature of superconductivity in HTSC because of decisive effect of dielectric permeability on electron-electron interactions.