Quasiparticles tunneling

The electron temperature was measured by superconductor-semiconductor-superconductor (S-Sm-S) junctions with Schottky barrier [7], In the S-Sm-S structure the quasiparticle tunneling across the junction is very sensitive to the electron temperature in the normal electrode and it can be used as an electron temperature probe with negligible heat leak. Bias current used for electron temperature measurements was few orders of magnitude smaller than the current used for the electron heating in Si film and therefore the possible heating by the bias current can be neglected. The S-Sm-S thermometers used in experiments were calibrated against the ruthenium oxide thermometer (see inset in Fig. 1). 

A Karpov, B Plathner, KH Gundlach, M Aoyagi, S Takada. Noise properties of a mixer with SIS NhN quasiparticle tunnel junctions. Proceedings of the 6th International Symposium on Space Terahertz Technology, Pasadena, CA, 1995. 

Fig. 4. Ground states of the grain before the quantum tunneling process (left) and after (right). The spin of the grain increases from zero to S during the tunneling process due to the quasiparticle exchange with the metallic plate.

The other important point is that the distribution function fn a) in the charge state n) is not assumed to be equilibrium, as previously (this condition is not specific to quantum dots with discrete energy levels, the distribution function in metallic islands can also be nonequilibrium. However, in the parameter range, typical for classical Coulomb blockade, the tunneling time is much smaller than the energy relaxation time, and quasiparticle nonequilibrium effects are usually neglected). 

Our result for RbaCeo differs from a recent determination by scanning tunneling microscopy [26] (A—77 K), possibly because NMR relaxation probes the minimum quasiparticle excitation energy, while tunneling probes the maximum in the quasiparticle density of states, or because of differences between surface and bulk properties. Our NMR relaxation data for Rb3C5o clearly deviate from an Arrhenius law below 8 K. At these tem-... 

This kind of semi-phenomenological theory is unsatisfactory from at least two points of view (1) No theory exists for the tunnel matrix elements that would take the complex quasiparticle structure on both sides in account and (2) the order parameter near the physical barrier behaves inhomogenously so that - if the corresponding regions are not formally included into the barrier - only the semiclassical theory of superconductivity appears appropriate (Ashauer et al. 1986). Furthermore, for reliable estimates of the size of tunnel currents, the orientation of interfaces relative to the crystal axes (Geshkenbein and Larkin 1986) and the influence of inhomogeneity on the spin-orbit coupling (Fenton 1985) may have to be taken properly into account. 

It is pointed out that the current-voltage characteristics below the gap are consistent with tunneling into d-wave superconductors. The tunneling quasiparticle current I V) is calculated using the expression... 

It has been argued that polarization acts as a potential well. Unfortunately, such a treatment tends to obscure the difference between a potential well for the electron and the total energy potential that is part of the Marcus model The nuclear reorganization of the nuclei appears to be omitted or built into the quasiparticle concept. Nuclear tunneling, leading to a larger rate at low temperatures, is easily confused with electron tunneling. 

Recently, direct measurements of the quasiparticle density of states (DOS) by scanning tunneling spectroscopy on Bi2Sr2CaCu20g+,5 (BSCCO-2212) single crystals as a function... 

In the last expression we have approximated g e) by its value at the Fermi level gp-The function g( ) is also plotted in Fig. 8.6. This is an intriguing result it shows that the superconducting state opens a gap in the density of states around the Fermi level equal to 2 A, within which there are no quasiparticle states. This is known as the superconducting gap and is directly observable in tunneling experiments. 

Another extension of this type of perturbation theory is to the case where there is some additional electronic order in the tip or the sample - for example, magnetic or superconducting order. In the case of magnetic order one is led to consider separate currents of spin-up and spin-down electrons, proportional to the spin-resolved components of the density of states. For a superconductor, the tunnel current depends on the quasiparticle density of states. 

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