Infrared properties of La₂₋ₓ(Ca,Sr)ₓCaCu₂O₆₊δ single crystals

الأصل · EN

The in-plane optical properties of two crystals of the bilayer cuprate, one with excess Ca and x=0.10 and the other with Sr and x=0.15, were investigated over the frequency range of 45--25000 cm⁻¹. The optical conductivity has been derived from Kramers-Kronig transformation. Each crystal exhibits a peak at around 15000 cm⁻¹ which corresponds to the charge-transfer gap of the parent insulator. With increasing carrier density, spectral weight shifts from the CT excitation to the low-ω region. For the superconducting sample (x=0.15), the optical conductivity displays a peak in the far-infrared region, which shifts toward zero frequency with decreasing temperature. The temperature-dependent behavior favors a dynamical localization picture. A ``pseudogap'' feature is observed in the low-frequency reflectance and the scattering rate spectra. Both the energy scale and the temperature dependence of the ``pseudogap'' are similar to other bilayer cuprates.