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'''Proximity effect''' or '''Holm-Meissner effect''' is a term used in the field of [[superconductivity]] to describe phenomena that occur when a superconductor (S) is placed in contact with a "normal" (N) non-superconductor. Typically the [[critical temperature]] <math>T_{c}</math> of the superconductor is suppressed and signs of weak superconductivity are observed in the normal material over [[Mesoscopic_physics|mesoscopic]] distances. The proximity effect is known since the pioneering work by R. Holm and W. Meissner.<ref name=Holm>{{Cite journal |author=Holm, R.; Meissner, W. |journal=Z.Physik. |year=1932 |volume=74 |page=715}}</ref> They have observed zero resistance in SNS pressed contacts, in which two superconducting metals are separated by a thin film of a non-superconducting (i.e. normal) metal. The discovery of the supercurrent in SNS contacts is sometimes mistakenly attributed to B. Josephson 1962 work, yet the effect was known long before his publication and was understood as the proximity effect.<ref name=Meis>{{Cite journal |author=Meissner, H. |title=Superconductivity in contacts with interposed barriers|journal=Phys.Rev. |year=1960 |volume=117 |pages=672–680}}</ref> | |||
==Origin of the effect== | |||
Electrons in a [[superconductor]] in the superconducting state are ordered in a very different way than in a normal metal, i.e. they are paired into cooper pairs. Furthermore, electrons in a material cannot be said to have a definitive position because of the momentum-position [[Complementarity_(physics)|complementarity]]. In solid state physics one generally chooses a momentum space basis, and all electron states are filled with electrons until the [[fermi surface]] in a metal, or until the gap edge energy in the superconductor. | |||
Because of the nonlocality of the electrons in metals, the properties of those electrons cannot change infinitely quickly. In the case of a superconductor and a normal metal, we have the superconducting cooper-paired-electrons order in the superconductor, and the gapless filled-up-to-the-fermi-surface electron order in the normal metal. if we bring the two together, the electron order in the one system cannot infinitely quickly (in real space) change into the other order at the border. The paired state in the superconducting layer is carried over to the normal metal, and there the pairing is destroyed by scattering events causing the paired electrons (cooper pairs) to lose coherence. For very clean metals like Cu it can be several hundreds of micrometers before the pairing is destroyed. | |||
Conversely, the (gapless) electron order present in the normal metal is also carried over to the superconductor in that the superconducting gap is lowered near the interface. | |||
The microscopic model describing this behavior in terms of single electron processes is called [[Andreev reflection]]. It describes how electrons in one one material "pick up" the order of the layer they are proximate to by taking into account which states are present in the other material to scatter from and taking into account effects as interface transparency. | |||
==Overview== | |||
As a contact effect, the SPE is closely related to thermoelectric phenomena like the [[Peltier effect]] or the formation of [[Semiconductors#P-N junctions|pn junctions]] in [[semiconductors]]. The proximity effect enhancement of <math>T_c</math> is largest when the normal material is a metal with a large diffusivity rather than an insulator (I). Proximity-effect suppression of <math>T_c</math> in a superconductor is largest when the normal material is ferromagnetic, as the presence of the internal magnetic field weakens superconductivity ([[Cooper pairs]] breaking). | |||
==Research== | |||
The study of S/N, S/I and S/S' (S' is lower superconductor) bilayers and multilayers has been a particularly active area of SPE research. The behavior of the compound structure in the direction parallel to the interface differs from that perpendicular to the interface. In [[type II superconductor]]s exposed to a magnetic field parallel to the interface, vortex defects will preferentially nucleate in the N or I layers and a discontinuity in behavior is observed when an increasing field forces them into the S layers. In type I superconductors, flux will similarly first penetrate N layers. Similar qualitative changes in behavior do not occur when a magnetic field is applied perpendicular to the S/I or S/N interface. In S/N and S/I multilayers at low temperatures, the long penetration depths and coherence lengths of the Cooper pairs will allow the S layers to maintain a mutual, three-dimensional quantum state. As temperature is increased, communication between the S layers is destroyed resulting in a crossover to two-dimensional behavior. The anisotropic behavior of S/N, S/I and S/S' bilayers and multilayers has served as a basis for understanding the far more complex critical field phenomena observed in the highly anisotropic cuprate [[High-temperature superconductivity|high-temperature superconductors]]. | |||
Recently the Holm-Meissner proximity effect was observed in [[graphene]] by the Morpurgo research group.<ref name=Morp>{{Cite journal |author=Heersche, H.B. et al. |title=Bipolar Supercurrent in Graphene|journal=Nature |year=2007 |volume=446 |pages=56–59|doi=10.1038/nature05555}}</ref> The experiments have been done on nanometer scale devices made of single graphene layers with superimposed superconducting electrodes made of 10 nm Ti and 70 nm Al films. Al is a superconductor, which is responsible for inducing superconductivity into graphene. The distance between the electrodes was in the range between 100 nm and 500 nm. The proximity effect is manifested by observations of a supercurrent, i.e. a current flowing through the graphene junction with zero voltage on the junction. By using the gate electrodes the researches have shown that the proximity effect occurs when the carriers in the graphene are electrons as well as when the carriers are holes. The critical current of the devices was above zero even at the Dirac point. | |||
==See also== | |||
*[[Andreev reflection]] | |||
==References== | |||
{{reflist}} | |||
*''Superconductivity of Metals and Alloys'' by [[Pierre-Gilles de Gennes|P.G. de Gennes]], ISBN 0-201-40842-2, a textbook which devotes significant space to the superconducting proximity effect (called "boundary effect" in the book). | |||
<br /> | |||
[[Category:Superconductivity]] | |||
Revision as of 14:45, 19 November 2013
Proximity effect or Holm-Meissner effect is a term used in the field of superconductivity to describe phenomena that occur when a superconductor (S) is placed in contact with a "normal" (N) non-superconductor. Typically the critical temperature of the superconductor is suppressed and signs of weak superconductivity are observed in the normal material over mesoscopic distances. The proximity effect is known since the pioneering work by R. Holm and W. Meissner.[1] They have observed zero resistance in SNS pressed contacts, in which two superconducting metals are separated by a thin film of a non-superconducting (i.e. normal) metal. The discovery of the supercurrent in SNS contacts is sometimes mistakenly attributed to B. Josephson 1962 work, yet the effect was known long before his publication and was understood as the proximity effect.[2]
Origin of the effect
Electrons in a superconductor in the superconducting state are ordered in a very different way than in a normal metal, i.e. they are paired into cooper pairs. Furthermore, electrons in a material cannot be said to have a definitive position because of the momentum-position complementarity. In solid state physics one generally chooses a momentum space basis, and all electron states are filled with electrons until the fermi surface in a metal, or until the gap edge energy in the superconductor.
Because of the nonlocality of the electrons in metals, the properties of those electrons cannot change infinitely quickly. In the case of a superconductor and a normal metal, we have the superconducting cooper-paired-electrons order in the superconductor, and the gapless filled-up-to-the-fermi-surface electron order in the normal metal. if we bring the two together, the electron order in the one system cannot infinitely quickly (in real space) change into the other order at the border. The paired state in the superconducting layer is carried over to the normal metal, and there the pairing is destroyed by scattering events causing the paired electrons (cooper pairs) to lose coherence. For very clean metals like Cu it can be several hundreds of micrometers before the pairing is destroyed.
Conversely, the (gapless) electron order present in the normal metal is also carried over to the superconductor in that the superconducting gap is lowered near the interface.
The microscopic model describing this behavior in terms of single electron processes is called Andreev reflection. It describes how electrons in one one material "pick up" the order of the layer they are proximate to by taking into account which states are present in the other material to scatter from and taking into account effects as interface transparency.
Overview
As a contact effect, the SPE is closely related to thermoelectric phenomena like the Peltier effect or the formation of pn junctions in semiconductors. The proximity effect enhancement of is largest when the normal material is a metal with a large diffusivity rather than an insulator (I). Proximity-effect suppression of in a superconductor is largest when the normal material is ferromagnetic, as the presence of the internal magnetic field weakens superconductivity (Cooper pairs breaking).
Research
The study of S/N, S/I and S/S' (S' is lower superconductor) bilayers and multilayers has been a particularly active area of SPE research. The behavior of the compound structure in the direction parallel to the interface differs from that perpendicular to the interface. In type II superconductors exposed to a magnetic field parallel to the interface, vortex defects will preferentially nucleate in the N or I layers and a discontinuity in behavior is observed when an increasing field forces them into the S layers. In type I superconductors, flux will similarly first penetrate N layers. Similar qualitative changes in behavior do not occur when a magnetic field is applied perpendicular to the S/I or S/N interface. In S/N and S/I multilayers at low temperatures, the long penetration depths and coherence lengths of the Cooper pairs will allow the S layers to maintain a mutual, three-dimensional quantum state. As temperature is increased, communication between the S layers is destroyed resulting in a crossover to two-dimensional behavior. The anisotropic behavior of S/N, S/I and S/S' bilayers and multilayers has served as a basis for understanding the far more complex critical field phenomena observed in the highly anisotropic cuprate high-temperature superconductors.
Recently the Holm-Meissner proximity effect was observed in graphene by the Morpurgo research group.[3] The experiments have been done on nanometer scale devices made of single graphene layers with superimposed superconducting electrodes made of 10 nm Ti and 70 nm Al films. Al is a superconductor, which is responsible for inducing superconductivity into graphene. The distance between the electrodes was in the range between 100 nm and 500 nm. The proximity effect is manifested by observations of a supercurrent, i.e. a current flowing through the graphene junction with zero voltage on the junction. By using the gate electrodes the researches have shown that the proximity effect occurs when the carriers in the graphene are electrons as well as when the carriers are holes. The critical current of the devices was above zero even at the Dirac point.
See also
References
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- Superconductivity of Metals and Alloys by P.G. de Gennes, ISBN 0-201-40842-2, a textbook which devotes significant space to the superconducting proximity effect (called "boundary effect" in the book).
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A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running
The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more
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In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang
Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules
Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.
A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running
The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more
There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang