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Microscopic gauge-invariant theory of the c-axis infrared response of bilayer cuprate superconductors and the origin of the superconductivity-induced absorption bands

  • Chaloupka, Jiří Department of Condensed Matter Physics, Faculty of Science, Masaryk University, Brno, Czech Republic
  • Bernhard, Christian Department of Physics and Fribourg Center for Nanomaterials, Switzerland
  • Munzar, Dominik Department of Condensed Matter Physics, Faculty of Science, Masaryk University, Brno, Czech Republic
    14.05.2009
Published in:
  • Physical Review B. - 2009, vol. 79, no. 18, p. 184513
Critical current density (superconductivity)
Fluctuations in superconductors
High-temperature superconductors
Josephson effect
Optical conductivity
Plasmons
Quasiparticles
Strong-coupling superconductors
Superconducting superlattices
English We report on results of our theoretical study of the c-axis infrared conductivity of bilayer high-Tc cuprate superconductors using a microscopic model involving the bilayer-split (bonding and antibonding) bands. An emphasis is on the gauge invariance of the theory, which turns out to be essential for the physical understanding of the electrodynamics of these compounds. The description of the optical response involves local (intrabilayer and interbilayer) current densities and local conductivities. The local conductivities are obtained using a microscopic theory, where the quasiparticles of the two bands are coupled to spin fluctuations. The coupling leads to superconductivity and is described at the level of generalized Eliashberg theory. Also addressed is the simpler case of quasiparticles coupled by a separable and nonretarded interaction. The gauge invariance of the theory is achieved by including a suitable class of vertex corrections. The resulting response of the model is studied in detail and an interpretation of two superconductivity-induced peaks in the experimental data of the real part of the c-axis conductivity is proposed. The peak around 400  cm⁻¹ is attributed to a collective mode of the intrabilayer regions, which is an analog of the Bogolyubov-Anderson mode playing a crucial role in the theory of the longitudinal response of superconductors. For small values of the bilayer splitting, its nature is similar to that of the transverse plasmon of the phenomenological Josephson superlattice model. The peak around 1000  cm⁻¹ is interpreted as a pair-breaking feature that is related to the electronic coupling through the spacing layers separating the bilayers.
Faculty
Faculté des sciences et de médecine
Department
Département de Physique
Language
  • English
Classification
Physics
License
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Persistent URL
https://folia.unifr.ch/unifr/documents/301196
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