← Back to Search
Tunneling Density Of States-Experiment
Published 1969 · Physics
In Chapter 19 of this volume Giaever showed how tunneling has been used to understand the properties of superconductors and measure the energy gap. In Chapter 21 Schrieffer presents a very elegant picture of what happens in the tunneling experiment when we take an electron from one metal and inject it into a superconductor where it can exist as a quasiparticle above or below the Fermi momentum k F . In this case of metal-to-superconductor tunneling, at 0°K the derivative of the tunneling characteristic in the superconducting state (dI/dV) S , divided by that in the normal state, (dI/dV) N , is simply N(E)/N(0), where N(E) is the density of excited allowed states in the superconductor and N(0) that in the normal metal. In this chapter I further discuss the development of the tunneling technique as a tool in the study of superconductivity, and I want to make the following three claims and try to substantiate them: 1. Tunneling is by far our most sensitive probe of the superconducting state. 2. Using tunneling we believe we have confirmed that the present theory of superconductivity is accurate to a few per cent, i.e., if we know a number of properties of the normal metal, then we can calculate the superconducting properties (T c , H c versus T, Δ 0, the tunneling characteristic, etc.) to an accuracy of a few per cent. Unfortunately, our knowledge of these required normal-metal properties is generally not as extensive as that of the superconducting properties. 3. Superconductivity, via an analysis of tunneling data, can tell us the normal-state properties mentioned in 2.