In-plane optical conductivity ofLa2−xSrxCuO4: Reduced superconducting condensate and

Abstract

Temperature dependences of the optical spectra of La2−xSrxCuO4 with x=0.12 and 0.15 were carefully examined for a polarization parallel to the CuO2-plane over a wide frequency range down to 8 cm −1 . Selection of well-characterized crystals enabled us to measure purely in-plane polarized spectra without any additional peak. The weight of superconducting (SC) condensate estimated from the missing area in σ1(ω) well agrees with the estimate from the slope of σ2(ω) vs 1/ω plot, showing no evidence that the Ferrell-Glover-Tinkham sum-rule is violated in the optical spectrum. We demonstrate that the optically estimated SC condensate is much smaller than the value obtained from the µSR measurement of magnetic penetration depth. We also find an anomalous increase of conductivity in sub-millimeter region towards ω=0 below Tc, which suggests the microscopic inhomogeneity in the superconducting state. Both observations are discussed in relation with the inhomogeneous electronic state that might be inherent to high-Tc cuprates.

Evidence for unusual superconducting correlations coexisting with stripe order inLa1.875Ba0.125CuO4

“…144͒ out to a hole concentration of at least 10%, and neutron-scattering studies 52,97,145 show that there is no true spin gap in the superconducting state for x Շ 0.13. Furthermore, the ratio of the superfluid density to the normal-state carrier density is observed 146,147 to be low in LSCO compared to other cuprates such as YBa 2 Cu 3 O 6+x , and a study 148 of the magnetic susceptibility of single crystals indicates that the Meissner fraction decreases with x for x Շ 0.09. Could these phenomena be associated with coexisting superconducting states?…”

Locating the Missing Superconducting Electrons in the Overdoped Cuprates La2−xSrxCuO4Mahmood1, He2, Božović3 et al. 2019Phys. Rev. Lett.8920802View full textAdd to dashboardCite

“…First, aside from the delta function at ν = 0, σ 1 (ν) for a dirty d -wave superconductor may be composed of both a narrow low frequency Drude-like peak and -if the normal state scattering rate is larger than the superconducting gap 2∆/h -a part that is an increasing function of ν (e.g., [23,24]). For weak-coupling d -wave BCS, 2∆ = 4.28k B T c and thus, 2∆/h is expected to range from 0.62 THz to 2.45 THz for the films studied here i.e., mostly within the spectral range of our spectrometer.…”

Submillimeter spectroscopy of materials with correlated electrons

“…The presented data were, in fact, first evidence for significant "subgap" absorption in HTSC cuprates. The nature of this phenomenon is unclear so far and is intensely studied with the use of a combination of infrared and BWT spectrometers [12]. As a tool for a study of charge dynamics in HTSC cuprates in the direction perpendicular to the CuO planes (along the c axis), attention has recently been drawn to specific plasma oscillations of Cooper pairs, which are called the Josephson plasmons.…”