Electron tunnelling spectroscopy

Abstract

The probability I + 12 of finding a conduction electron a distance t outside a metal even at very low temperatures is not zero, but is governed by the metal's work function C#I through an exponential law I #I 1 2 N exp ( -Z K t ) , with K 2: (2m/h2)1/2 C#IW. This basic consequence of quantum mechanics makes possible measurable electrical currents between two conductors separated by a sufficiently thin uniform ( -20 A) insulator.The energy-spectroscopic information that can be, and has been, derived from careful measurement of the current-voltage (I-V) relation in such experiments is the subject of the present review. I n probably the most important application of the technique Giaever in 1960demonstrated that when one member of the junction is superconducting, the differential conductance d1jdV as a function of bias energy eV directly measures the density of quasiparticle excitations of the superconductor. Such data are shown to permit the most complete characterisation of the strong coupling superconducting state that is presently available, and have contributed in a most important way to our present understanding of superconductivity and superconductors.

Very-low-temperature tunneling spectroscopy in the heavy-fermion superconductorPrOs4Sb12

“…Therefore, we can take 190mK as the lowest measuring temperature that can be achieved at present with our set-up. Our resolution is similar to the one achieved in many planar junction experiments [17], with the important difference that in STM measurements the tunnelling current is between 4 to 6 orders of magnitude smaller.…”

Dynamics of nonequilibrium quasiparticles in narrow-gap superconducting tunnel junctions

“…1 There is currently great interest in using high quality superconducting tunnel junctions as single photon detectors for astrophysical and other applications. 2 Such detectors operate under highly nonequilibrium conditions which do not occur in any other experimental scenario.…”

Proximity electron tunneling spectroscopy I. Experiments on Nb

“…Here Wlog= exp (In w) and averages (f(w)) are computed as (f(to)) = ~ f(w)oeZF(og) d In o~ (4) In particular, the average (w 2) is related to A via the McMillan relation z (5) where N(0) is the density of states of one spin index at the Fermi level, M is the atomic mass, and (i2) is an averaged squared matrix element. Evidently the key to this analysis is the Eliashberg function a2F(oJ), which is most directly measured by Giaever-McMillan-Rowell tunneling spectros-1,4,~ copy.…”