Ultrasonic attenuation of longitudinal and shear waves in superconducting lead |
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Authors: | Jacob Philip B K Basu K Samudravijaya |
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Affiliation: | (1) Department of Physics, Cochin University, Cochin, India;(2) Tata Institute of Fundamental Research, Bombay, India |
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Abstract: | Longitudinal and shear wave ultrasonic attenuations have been measured in high-purity Pb on two single crystals obtained from the same ingot. The measurements were done at low temperatures, at different frequencies, and in transverse magnetic fields, up to a field of 7.3 kG. The propagation directions in the two crystals were along 100] and 110]. For some propagation and polarization directions the
s
/
n
ratio is found to be frequency-independent, while for others, large divergences in the
s
/
n
ratios at different frequencies are observed. A sharp decrease of
s
/
n
nearT
c
is observed for a particular longitudinal wave propagation, but not in any shear wave propagation. In some cases
s
/
n
is found to be abnormally high and this feature is associated with a peak in attenuation
n
and a relatively high
n
at 7.2 K. None of the
s
/
n
curves fits closely to any BCS energy gap. For longitudinal waves the high magnetic field (H) dependence of the normal state attenuation was found to agree qualitatively with the free electron theory for propagation along 100], but not for propagation along 110]. For shear waves the high-field attenuations do not extrapolate to zero asH tends to infinity. For all propagation and polarization directions the high-field attenuations show 1/H
2 field dependence. |
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Keywords: | |
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