Correlation between the Josephson coupling energy and the condensation energy in bilayer cuprate superconductors

Abstract

We review some previous studies concerning the intra-bilayer Josephson plasmons and present new ellipsometric data of the c-axis infrared response of almost optimally doped Bi2Sr2CaCu2O8. The c-axis conductivity of this compound exhibits the same kind of anomalies as that of underdoped YBa2Cu3O 7−δ . We analyze these anomalies in detail and show that they can be explained within a model involving the intra-bilayer Josephson effect and variations of the electric field inside the unit cell. The Josephson coupling energies of different bilayer compounds obtained from the optical data are compared with the condensation energies and it is shown that there is a reasonable agreement between the values of the two quantities. We argue that the Josephson coupling energy, as determined by the frequency of the intra-bilayer Josephson plasmon, represents a reasonable estimate of the change of the effective c-axis kinetic energy upon entering the superconducting state. It is further explained that this is not the case for the estimate based on the use of the simplest "tight-binding" sum rule. We discuss possible interpretations of the remarkable agreement between the Josephson coupling energies and the condensation energies. The most plausible interpretation is that the interlayer tunneling of the Cooper pairs provides the dominant contribution to the condensation energy of the bilayer compounds; in other words that the condensation energy of these compounds can be accounted for by the interlayer tunneling theory. We suggest an extension of this theory, which may also explain the high values of Tc in the single layer compounds Tl2Ba2CuO6 and HgBa2CuO4, and we make several experimentally verifiable predictions. determines U 0 . Van der Marel and Tsvetkov [12] proposed a phenomenological model of the dielectric response of such a superlattice of inter-bilayer and intra-bilayer Josephson junctions. They showed that it exhibits a transverse resonance between the two zero crossings corresponding to the two plasmons. It has been suggested [13] that this new excitation ("transverse plasma excitation"), which can be visualized as a resonant oscillation of the condensate density between the two closely spaced copper-oxygen planes, has indeed been observed as an additional absorption peak which appears at low temperature in the spectra of the infrared c-axis conductivity of underdoped Y123 [14,15,16,17]. Very recently, this interpretation has been put on a firm basis by a detailed analysis of the c-axis conductivity data for Y123 with different oxygen concentrations [18,19]. Note that the observation of the transverse plasma excitation also implies the existence of the second (intra-bilayer) Josephson plasmon which is a vital ingredient of the ILT theory. This opens a possibility to test also for bilayer compounds the relationship between the Josephson coupling energy and the condensation energy predicted by the ILT theory (Eq. (1)).In this paper we review some of the previous experimental observations of the transverse plasma excitatio...

Phonon anomalies in trilayer high-Tc cuprate superconductors

“…(22), see Appendix. In the previous works concerning bilayer systems Y-123 [14] and Bi-2212 [5,23], α and β have been calculated using the second approach but j ph using the first one, i.e., Eq. (22).…”

Josephson Plasma Resonance and Phonon Anomalies in TrilayerBi2Sr2CaBoris1, Munzar2, Kovaleva3 et al. 2002Phys. Rev. Lett.441360View full textAdd to dashboardCite

“…A similar absorption band has been previously identified in the bilayer compound Y123 where it has been assigned [5,6,7] to the t-JPR of the JSM. While this feature is rather weak in Bi2212 [8,9], its SW is very large in Bi2223 and gives rise to a considerable increase in the FIR-SW below T c . This is evident from Fig.…”

“…Their out-of-phase oscillation gives rise to a transverse Josephson-plasma resonance (t-JPR) which has been assigned to the absorption peak that develops below T c . This model, termed Josephson-superlattice-model (JSL) in the following, has been successfully applied to describe the anomalous FIR c axis response of Y123 and [5,6,7,8,9]. Nevertheless, it is not commonly accepted yet, and it is even disputed whether the SW of the absorption band is electronic in origin, and whether it arises from higher frequencies [11].…”

“…For the bilayer systems Y123 and Bi2212 it has already been shown that a sizeable absorption peak develops below T c in the FIR range. Evidence has been presented that its SW is mostly electronic in origin and that it is part of the SC condensate [5,6,7,8,9]. This can be understood in terms of the interlayer-tunneling (ILT) model [3] which assumes that the CuO 2 planes are weakly coupled by the Josephson-currents in the SC state.…”

“…Except for the additional modes of Bi2223 at 400 cm −1 and 128 cm −1 IR-active phonons appear in Bi2212 at similar frequencies [8,9]. In order to find the corresponding eigenvector patterns we have performed shell model calculations for the Bi-based compounds in the body centered tetragonal I4/mmm structure.…”