Effect of Hydrostatic Pressure on Superconducting LeadIndium Alloys Using Electron Tunneling
Abstract
The effect of pressure on the effective phonon spectrum α^{2}(ω)F(ω), the dimensionless electronphonon interaction strength λ, and the average electronphonon coupling function <α^{2}> has been determined in the superconducting alloys Pb_{95}In_{5} and Pb_{88}In_{12}. Electrontunneling measurements at pressures from 0 to 3600 bar provided the energy gap and tunneling density of states which served as input to McMillan's gap inversion program which calculated α^{2}(ω)F(ω), λ, and <α^{2}>. Pressure production was via solid helium which provided nearly hydrostatic pressures. The energy gap decreases and the phonon frequencies increase with increasing pressure. The impurity band undergoes the smallest relative shift with increasing pressure and the transverse peak exhibits the largest relative shift. α^{2}(ω)F(ω) shifts toward higher frequencies and decreases slightly in amplitude. The net result of all these effects is for a shift of the electronphonon interaction toward weaker coupling. The best indicators of this trend are the observed decrease of λ and <α^{2}> with increasing pressure. These values are dlnλdP=7.9×10^{6} bar^{1} and dln<α^{2}>dP=3.2×10^{6} bar^{1} for Pb_{88}In_{12}. The values for Pb_{95}In_{5} are close to these. The pressure dependence of γ, the electronicspecificheat coefficient, determined from the pressure dependence of the quanity Z_{n}(0)=1+λ, gives a value close to that of Pb determined from thermalexpansion measurements and from recent theoretical considerations.
 Publication:

Physical Review B
 Pub Date:
 August 1973
 DOI:
 10.1103/PhysRevB.8.1042
 Bibcode:
 1973PhRvB...8.1042H