Hamburg 2001 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 4: Josephson Kontakte

TT 4.5: Vortrag

Montag, 26. März 2001, 15:45–16:00, J

Optical Response of the Josephson Plasma Resonance and Phonons — •Christian Helm and L.N. Bulaevskii — Los Alamos National Laboratory, Los Alamos, NM 87501

The frequency dependent reflectivity R(ω) and transmission T( ω ) of a stack of weakly coupled layered superconductors are calculated near the Josephson plasma resonance both in systems with identical junctions (Tl-2201) and with alternating plasma frequencies (LaSmCuO₄). The superconducting layers are coupled both inductively and due to charging of the layers, which leads to a finite width of the plasma band in the c-direction. In contrast to the dispersionless case, all modes in the plasma band are excited by the incident electromagnetic wave despite the fact that it has a definite small wave vector. The spectrum is insensitive to the number of junctions and the eigenvectors of the plasma mode turn out to have different amplitudes on the surface. As a consequence, they contribute unequally to R and T, which is essential for determining the frequency interval where R(ω)<1 or T(ω)>0 correctly. This effect is not taken into account in the conventional Fresnel formulas for R(ω) and T(ω). The analogous phenomenon is studied for the optical spectroscopy of of phonons with dispersion.