Signatures of the bonding-antibonding splitting in the c-axis infrared response of moderately underdoped bilayer and trilayer cuprate superconductors

Abstract

We report on results of our analysis of the c-axis infrared conductivity, σc(ω), of bilayer LnBa2Cu3O7−δ (Ln=La, Nd, Y) and trilayer Bi2Sr2Ca2Cu3O10+δ high-Tc superconductors. The analysis employs the multilayer model involving the conductivity of the bilayer or trilayer unit, σbl(ω), and that of the spacing layers separating the latter units, σint(ω). For the YBa2Cu3O7−δ sample with concentration of holes p=0.09, our fitting of the data strongly suggests that at low temperatures, the conductivity σbl(ω) possesses a pronounced and narrow Drude peak. For samples with p≥0.115 however, the fitting indicates that σbl(ω) is, at low temperatures, dominated by a mode at a finite energy in the range from 30 to 60 meV. The properties of this resonance are in accord with those of a collective mode that appears in the spectra of σbl(ω) calculated using a microscopic gauge-invariant theory of σc(ω) by J. Chaloupka and coworkers [Phys. Rev. B 79, 184513 (2009)]. The frequency and spectral weight of the latter mode are determined by the magnitude of the splitting between the bonding and the antibonding band of the bilayer or trilayer unit. Our results, in conjunction with the microscopic theory, thus demonstrate that in moderately underdoped bilayer and trilayer high-Tc cuprates the bilayer (or trilayer) splitting is already developed. The observed doping dependence is consistent with results from angular resolved photoemission spectroscopy.

Source-reported materials — not catalogue approval

Similar papers