Superconducting proximity effect

There s also the possibility that the silver mixture will allow the superconducting proximity effect to occur. (Superconductivity can occur between two superconductors that are physically separated so long as the barrier is a conducting metal.) That tunneling effect may be the key to developing materials that can be machined, drawn into wires, or cast into various production shapes. Preliminary experiments have shown that the new silver composite is quite strong and can be machined into several useful forms. 

H. Takayanagi and T. Kawakami, Superconducting Proximity Effect in the Native Inversion Layer on InAs, Phys. Rev. Lett. 54, 2449 (1985). 

JJl, Varela, M, Prieto, P, Leon, C, Martinez, JX, and Santamaria, J. (2003) Fetromagnetic/superconducting proximity effect in Lao.7Caa3Mn03/YBa2Qi307- superlattices. Phys. Rev. B, 67, 214511. 

When a normal metal and a superconductor are in intimate contact with each other, there can be a leakage of the superconducting Cooper pairs from the superconductor to the normal metal and quasiparticle (normal electron) leakage from the metal to the superconductor. This effect is known as the superconducting proximity effect and is an important phenomenon that can be used in practical applications such as in electronic devices and as a tool to better understand superconductivity [64J. The proximity effect can occur over distances that are quite large compared to molecular dimensions. Cooper pairs typically extend into normal metals for distances on the order of 100 nm and, in some cases, considerably further. 

M. Hatano, T. Nishino, and U. Kawabe, Experiments of the superconducting proximity effect between superconductor and semiconductor, Appl. Phys. Lett. 50 52 (1987). 

In the SRM-768, this effect is reduced by spot welding small pieces of A1 to the W and Be samples. The Al, with its Tc = 1.18 K, serves as a nucleation centre to induce superconductivity in the samples by proximity effect (see Section 15.2.2). 

In a normal metal (N) coupled to a superconductor (S), superconducting properties are locally induced by the proximity effect. The characteristic energy scale of this proximity superconductivity is given by the minimum of the bulk superconductor energy gap A and the Thouless energy ec ... 

One issue of importance for these superconducting FETs is the attainment of very low contact resistance from the source or drain to the channel. Obviously, poor contacts will inhibit the induction of superconductivity via the proximity effect into the channel. If low, or zero, contact resistance can be achieved, this could give a valuable contribution to the performance of an FET even without the channel becoming superconducting. 

Electrical properties of junctions formed between superconducting material, S, and a non-superconducting metallic material, N, which may be a metal or a degenerate semiconductor, are determined by special boundary conditions. If we consider a superconductor-semiconductor (S-N) interface with high transparency, a proximity effect is observed due to injection of electron pairs (Cooper pairs) from the superconductor into the semiconductor where they decay over a characteristic length, the induced coherence length. 

When a superconductor S is brought into a contact with a non superconducting (normal) metal N the proximity effect mainly defines the properties of this hybrid structure. The concept of the proximity effect is related to the diffusive penetration of the Cooper pairs from S to N metal over some distance [1]. The condensate wave function monotonically decays in the normal metal due to the finite lifetime of superconducting electrons in it. The characteristic distance of the wave function decay is the coherence length gN = hDNl2tikBT)m, where DN is the diffusion coefficient of N metal, and T is the temperature. The %N values are usually order of dozens of nanometers [2]. When the N layer in a S/N proximity effect structure is replaced by a metallic ferromagnet F, the pair wave function from S still penetrates in F and makes the F layer superconducting. 

For a unique interpretation of these interesting experimental results, some new developments in theory would be highly desirable. These concern a realistic description of tunnel barriers within the semiclassical approach to superconductivity. Although it is possible within this theory to treat the standard surface model for the proximity effect with help of a sensible phenomenological boundary condition (Ashauer et al. 1986), tunnelling through a barrier is usually described... 

These observations also suggest that the [T10]oo and [BiO]oo layers are not insulating layers but exhibit a metallic or a semi-metallic character and can become superconductive at low temperature by proximity effect... 

This chapter is divided into a number of sections that describe important details related to the conductive polymer/superconductor structures. First, information is provided concerning the preparation and characterization of various polymer/superconductor structures. Chemical and electrochemical deposition methods for localizing the polymers onto a number of cuprate phases are discussed. Section III is devoted to relevant background information related to the induction of superconductivity into metals and semiconductor systems via the proximity effect. More specifically, the four basic methods that have been used to study the occurrence of proximity effects in classical solid-state conductors are described (i.e., contact resistance, modulation of superconductivity in normal/superconductor bilayer structures, passage of supercurrent through superconductor/ normal/superconductor systems, and theoretical analyses). Sections IV and V are devoted to experimental studies of conductive polymer/superconductor interface resistances and modulation of superconductivity in the hybrid systems. Finally, there is a discussion of the initial experimental results that explores the possible induction of superconductivity into organic materials. 

Having identified methods to deposit conductive polymer and molecular metal systems onto cuprate superconductor structures without damage to either material, it becomes important now to consider the electronic interactions that occur when the two conductors are in contact with one another. Of particular importance is the interaction that occurs between the polymer-derived charge carriers and the superconducting Cooper pairs. Important background information related to this area can be obtained from the well-documented behavior of the more classical metal/superconductor and semicon-ductor/superconductor systems. Thus, prior to considering experimental data and theoretical treatments for organic conductor proximity effects, we review previous studies of proximity effects in the more classical systems. 

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