Junction normal-metal - superconductor

A number of researchers have investigated the contact resistance phenomena that occur between high temperature superconductors and conventional materials [63,86-90]. Low contact resistance values are necessary for many practical applications. High contact resistance values can lead to local heating and the loss of superconductivity at the contact interface. In addition, future applications may involve the use of superconductor/ normal metal/superconductor (S-N-S) Josephson junctions, and these devices can be fabricated only with materials that exhibit low contact resistance values. 

Tunneling electric current through the normal metal insulator superconductor junction is accompanied with heat flow out of normal metal when property voltage is biased. The phenomenon enables cooling of electrons and phonons (under special conditions) in the region below 1K. At lower bath temperatures, two parasitic heat sources decrease refrigerator performance ... 

A Josephson junction consists of two closely spaced superconductors separated by a weak connection (Figure 4.6.1). This connection may be provided by an insulator, a normal metal, a semiconductor, a weakened superconductor, or some other material that weakly couples the two superconductors. The two superconducting regions may be characterized by quantum mechanical wave functions and 2 respectively. Normally a much more complicated description would be necessary because... 

The tunneling process across a SIN (superconductor-insulator-normal metal) junction is more complicated than across a NIN (normal metal-insulator-normal metal) junction described in sec. 3.2. An electron reacliing an insulator (1) from a normal metal (N) takes either one of four elementary processes, i.e., (1) reflection as an electron... 

Much of the interest in superconductor components revolves around the central issue that below a characteristic temperature, Tc, superconductors exhibit zero resistance to the flow of electricity figure 1 A). Above this temperature, the material behaves as a normal metal wherein isolated electrons (or holes) carry the charge with finite resistance. Below Tc, however, the electrons form loosely associated pairs which are responsible for all the superconducting properties. At temperatures close to Tc, only a minute fraction of the conduction electrons form the Cooper pairs (Figure IB). Under such circumstances, superconductivity is easily disrupt by heati light, and magnetic fields. Creation of weakly coupled superconductor structures such as Josephson junctions, serves to further increase the sensitivity of the superconductor components. It is this sensitivity to external stimuli that provides the basis for the preparation of a variety of superconductor-based detectors and devices. 

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