Abstract
Differential resistance measurements of Nb-insulator-lead tunnel junctions as a function of dc bias voltage are reported. The amplitude of the charge-density-wave gap, , which occurs in Nb at K is found equal to 70 ± 5 meV. This value decreases when pressure is applied but the ratio is pressure independent up to 2.5 kbars. This large magnitude of the charge-density-wave gap, at variance with the BCS value, is interpreted as resulting from the strong-coupling nature of electron-phonon interactions.
- Received 25 July 1986
DOI:https://doi.org/10.1103/PhysRevLett.57.2199
©1986 American Physical Society