Polarization-dependent infrared reflectivity study of Sr${}_{2.5}$Ca${}_{11.5}$Cu${}_{24}$O${}_{41}$ under pressure: Charge dynamics, charge distribution, and anisotropy

Abstract

We present a polarization-dependent infrared reflectivity study of the spin-ladder compound Sr${}_{2.5}$Ca${}_{11.5}$Cu${}_{24}$O${}_{41}$ under pressure. The optical response is strongly anisotropic, with the highest reflectivity along the ladders/chains (\textbf{E}$\Vert$c) revealing a metallic character. For the polarization direction perpendicular to the ladder plane, an insulating behavior is observed. With increasing pressure the optical conductivity for \textbf{E}$\Vert$c shows a strong increase, which is most pronounced below 2000~cm${}^{-1}$. According to the spectral weight analysis of the \textbf{E}$\Vert$c optical conductivity the hole concentration in the ladders increases with increasing pressure and tends to saturate at high pressure. At $\sim$7.5~GPa the number of holes per Cu atom in the ladders has increased by $\Delta \delta$=0.09 ($\pm$0.01), and the Cu valence in the ladders has reached the value +2.33. The optical data suggest that Sr${}_{2.5}$Ca${}_{11.5}$Cu${}_{24}$O${}_{41}$ remains electronically highly anisotropic up to high pressure, also at low temperatures.

9 pages, 9 figures; submitted to Phys. Rev. B

References in corpus (3)

• Pressure-induced deconfinement of the charge transport in the quasi-one-dimensional Mott insulator (TMTTF)_2AsF_6
• Influence of doping on the Hall coefficient in Sr_{14-x}Ca_xCu_24O_41
• Suppression of the Charge-Density-Wave State in Sr${}_{10}$Ca${}_4$Cu${}_{24}$O${}_{41}$ by External Pressure

Cited by in corpus (1)

• Valence Transition Theory of the Pressure-Induced Dimensionality Crossover in Superconducting Sr${}_{14-x}$Ca${}_x$Cu${}_{24}$O${}_{41}$