Superconducting energy gap and normal-state conductivity of a single-domain<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">YBa</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">Cu</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>7</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>crystal

Abstract

Using polarized reflectivity measurements of single-domain crystals, we are able to distinguish chain and plane contributions to the infrared conductivity of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$. A substantial chain contribution to \ensuremath{\sigma}(\ensuremath{\omega}) persisting to low frequency and temperature is observed. For the intrinsic conductivity of the ${\mathrm{CuO}}_{2}$ planes a superconducting energy gap of 500 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ (2\ensuremath{\Delta}/${\mathit{kT}}_{\mathit{c}}$\ensuremath{\simeq}8) is evident in the infrared data, while the normal-state conductivity drops much more slowly with \ensuremath{\omega} than the ordinary Drude form, and can be described in terms of a scattering rate \ensuremath{\Elzxh}/${\mathrm{\ensuremath{\tau}}}^{\mathrm{*}}$\ensuremath{\sim}kT+\ensuremath{\Elzxh}\ensuremath{\omega} at low frequency. The former result (2\ensuremath{\Delta}/${\mathit{kT}}_{\mathit{c}}$\ensuremath{\simeq}8) suggests suppression of ${\mathit{T}}_{\mathit{c}}$; the latter, that ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ is not an ordinary Fermi liquid.