The temperature dependences of the linewidths and frequencies of the 340-, 440-, and 500-

{cm}^{- 1}

Raman-active phonons have been measured in lightly twinned single crystals of

{YBa}_{2}

{Cu}_{3}

O_{y}

with different oxygen concentrations y. The observed superconductivity-induced changes in the linewidths and frequencies that occur for temperatures below the critical temperature have been found to depend on the oxygen concentration within the range 6.7≲y≲7.0, with the most sensitive dependence occurring in the 340-

{cm}^{- 1}

phonon-linewidth variations near y≊7.0. The linewidth and frequency dependences of the 340-

{cm}^{- 1}

B_{1 g}

mode for T<

T_{c}

suggest that the redistribution of electronic states below

T_{c}

is very sensitive to the oxygen or hole concentration within this range. Estimates for the superconducting energy gap 2Δ have been obtained from comparisons of the temperature dependence of the 340-

{cm}^{- 1}

mode with strong-coupling theory and these indicate that 2Δ increases as the oxygen or hole concentration y decreases from y=7.0 where 2Δ≊5.4 k

T_{c}

. The linewidth and frequency of the 440-

{cm}^{- 1}

A_{g}

mode are, however, relatively insensitive to variations in y and it is suggested that the 440- and 500-

{cm}^{- 1}

phonons couple to a different set of electrons than does the 340-

{cm}^{- 1}

mode.

Publications with shared reference:

0 publications found