Abstract
We report on measurements of the differential conductivity of contacts, which reveal the existence of low-energy Andreev surface bound states. These bound states are identified via huge conductance peaks at zero bias that may form only in superconductors with nontrivial energy-gap functions. From the voltage dependence of at we also establish a lower limit of the normalized energy gap, such that , much in excess of the weak coupling BCS value of 3.5, and directly indicating strong coupling effects in superconducting .
- Received 30 November 1999
DOI:https://doi.org/10.1103/PhysRevLett.84.5616
©2000 American Physical Society