Determination of the optical properties of La2−xBaxCuO4

Abstract

The optical properties of single crystals of the high-temperature superconductor La2−xBaxCuO4 have been measured over a wide frequency and temperature range for light polarized in the a-b planes and along the c axis. Three different Ba concentrations have been examined, x = 0.095 with a critical temperature Tc = 32 K, x = 0.125 where the superconductivity is dramatically weakened with Tc ≃ 2.4 K, and x = 0.145 with Tc ≃ 24 K. The in-plane behavior of the optical conductivity for these materials at high temperature is described by a Drude-like response with a scattering rate that decreases with temperature. Below Tc in the x = 0.095 and 0.145 materials there is a clear signature of the formation of a superconducting state in the optical properties allowing the superfluid density (ρs0) and the penetration depth to be determined. In the anomalous 1/8 phase, some spectral weight shifts from lower to higher frequency ( 300 cm −1 ) on cooling below the spin-ordering temperature Tso ≃ 42 K, associated with the onset of spin-stripe order; we discuss alternative interpretations in terms of a conventional density-wave gap versus the response to pairdensity-wave superconductivity. The two dopings for which a superconducting response is observed both fall on the universal scaling line ρs0/8 ≃ 4.4σ dc Tc, which is consistent with the observation of strong dissipation within the a-b planes. The optical properties for light polarized along the c axis reveal an insulating character dominated by lattice vibrations, superimposed on a weak electronic background. No Josephson plasma edge is observed in the low-frequency reflectance along the c axis for x = 1/8; however, sharp plasma edges are observed for x = 0.095 and 0.145 below Tc.

Neutron-Scattering Evidence for a Periodically Modulated Superconducting Phase in the Underdoped CuprateLa1.905Ba0.095CuO4Xu1, Stock2, Chi3 et al. 2014Phys. Rev. Lett.3014341View full textAdd to dashboardCite

“…To generate this large a response, we conclude that all parts of the sample must contribute to the signal, ruling out macroscopic phase separation. A previous optical conductivity study has shown that the superfluid density of this sample is consistent with the trend established for bulk superconductivity in all cuprate families in the form of Homes' law [19]. It thus appears that there must be local coexistence of the spin fluctuations and superconductivity.…”

Transport properties of stripe-ordered high Tc cuprates

“…2(c), appears to frustrate the interlayer Josephson coupling. A similar conclusion is indicated by optical conductivity studies [39,40]. Mean-field 2D superconductivity sets in at T 2D c together with the spin stripe order (T so ), with the resistivity staying finite until phase order is established at T BKT .…”

Simulation of a hump structure in the optical scattering rate within a generalized Allen formalism and its application to copper oxide systems

“…1). This feature in reflectance spectra of the peak+dip case looks similar that of electron underdoped cuprates and hole doped cuprates [7,5,34,32,6,8] (see also Fig. 5 for closer comparisons).…”

“…(2). More explicitly we can write down the real and imaginary parts of the optical conductivity as a function of the real and imaginary parts of the optical self energy as [6] and with measured hole underdoped data of La 1.875 Ba 0.125 CuO 4 (middle column) [32,8]. In the middle column the scales on the vertical axis are shown on the right side.…”