Phonon anomalies in trilayer high-Tc cuprate superconductors

Abstract

We present an extension of the model proposed recently to account for dramatic changes below T c (anomalies) of some c-axis polarized infrared-active phonons in bilayer cuprate superconductors, that applies to trilayer high-T c compounds. We discuss several types of phonon anomalies that can occur in these systems and demonstrate that our model is capable of explaining the spectral changes occurring upon entering the superconducting state in the trilayer compound Tl 2 Ba 2 Ca 2 Cu 3 O 10 . The low-temperature spectra of this compound obtained by Zetterer and coworkers display an additional broad absorption band, similar to the one observed in underdoped YBa 2 Cu 3 O 7−δ and Bi 2 Sr 2 CaCu 2 O 8 . In addition, three phonon modes are strongly anomalous. We attribute the absorption band to the transverse Josephson plasma resonance, similar to that of the bilayer compounds. The phonon anomalies are shown to result from a modification of the local fields induced by the formation of the resonance. The spectral changes in Tl 2 Ba 2 Ca 2 Cu 3 O 10 are compared with those occurring in Bi 2 Sr 2 Ca 2 Cu 3 O 10 , reported recently by Boris and coworkers.

Evidence of a Precursor Superconducting Phase at Temperatures as High as 180 K inRBa2Cu3O7−δ (R=<

“…Figure 3(a) shows the 10 K spectra which demonstrate that the strongest feature is associated with the phonon mode at 185 cm −1 . This is not surprising since this phonon exhibits large temperature dependent changes that are accounted for by the MLM [29] and thus are associated with the intra-bilayer currents. Accordingly, it provides a sensitive indicator to test whether the magnetic field has a similar effect on the coherency of the electronic state at T c < T < T ons as it has at T < T c .…”

Pseudogap and precursor superconductivity in underdoped cuprate high temperature superconductors: A far-infrared ellipsometry study

“…Accordingly, it is responsible for the anomalous temperature dependence of some of the infrared-active c-axis phonon modes. It was indeed shown that the MLM provides an excellent description not only of the TPM but also of the sizeable anomalies of the c-axis phonon modes [46][47][48]64]. It turns out that the renormalization of the phonons is directly linked with the charge oscillations.…”

“…A detailed derivation of the equations can be found in Ref. [48]. The c-axis dielectric function in the optical limit is expressed as…”

“…While the fits could be improved by allowing several type of ions to vibrate, as in Ref. [47,48], this would mostly increase the complexity of the model but hardly yield more accurate results for the local conductivity, σ bl , which is the main subject of the present work.…”

“…We show that the information about the precursor superconducting state is contained in an electronic mode, the so-called transverse plasma mode (TPM), and in the related anomalous temperature dependence of some infrared-active phonons, which have been previously identified [22,23,36,43]. It is meanwhile well established that both of these features can be well described with the so-called multilayer model (MLM) [43][44][45][46][47][48] where the difference between the electronic response of the bilayer region and that of the inter-bilayer region is taken into account and described in terms of the local conductivities, σ bl and σ int , respectively. Below we outline how the characteristic frequency-and temperature dependence of σ bl and σ int can be derived with the MLM and can be used to disentangle the properties and, in particular, the onset temperatures of the precursor superconducting state and the competing pseudogap, T ons and T * , respectively.…”