Abstract
We have studied the development of the optical conductivity as electrons are added to the Cu-O planes in ${\mathrm{Pr}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ce}}_{\mathit{x}}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ by varying x(0\ensuremath{\le}x\ensuremath{\le}0.2). In the metallic phases, contributions to the optical conductivity below 3 eV arise from three sources: mobile carriers, mid-infrared excitations, and charge-transfer excitations. The mobile carrier spectral weight grows roughly linearly with x, while the mid-infrared band appears to evolve at low doping via a transfer of spectral weight from the charge-transfer band. Comparing these results with hole doping in ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_{4\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ indicates an electron-hole symmetry that is not anticipated by standard charge-transfer insulator models.
Highlights
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We have studied the development of the optical conductivity as electrons are added to the Cu
Summary
The Rapid Communications section is intended for the accelerated publication of important new results g.ince manuscripts. The mobile carrier spectral weight grows roughly linearly with x, while the mid-infrared band appears to evolve at low doping via a transfer of spectral weight from the charge-transfer band. Comparing these results with hole doping in. In spite of much study, little is understood about either ' the normal-state excitation spectrum of the high-T, compounds, or the manner in which this spectrum develops from the insulating phase as a function of doping We address these issues here in an optical-reflectivity study of n type Pr2--, Ce„Cu04 —s for 0&x &0.2 and b-0. At x 0, Pr2 „Ce,Cu04 s is an insulator with negligible (x-0. absorption below the charge-transfer gap (to-1.5 eV)
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