A state in which the electrical resistance of a material is so low that it cannot be measured and appears to be zero refers to superconductivity the aid materials are called as super conductors .The superconducting state is also characterized by unusual magnetic properties. Superconductivity is a condition in which many metals, alloys, organic compounds, and ceramics conduct electricity without resistance, usually at low temperatures. Heinke Kamerlingh Omnes, a Dutch physicist, discovered superconductivity in 1911.
Superconductivity was discovered by H. Kamerlingh-Onnes in Holland in 1911 as a result of his investigations leading to the liquefaction of helium gas. In Onnes' time superconductors were simple metals like mercury, lead, bismuth etc. These elements become superconductors only at the very low temperatures of liquid helium. During the 75 years that followed, great strides were made in the understanding of how superconductors worked. Over that time, various alloys were found that were superconductors at somewhat higher temperatures. Unfortunately, none of these alloy superconductors worked at temperatures much more than 23 Kelvin. Thus, liquid helium remained the only convenient refrigerant that could be employed with these superconductors. Then in 1986, researchers at an IBM laboratory in Switzerland, discovered that ceramics from a class of materials called perovskites were superconductors at a temperature of about 35 Kelvin. This event sparked great excitement in the world of physics, and earned the Swiss scientists a Nobel prize in 1987. As a result of this breakthrough, scientists began to examine the various perovskite materials very carefully. In February of 1987, a perovskite ceramic material was found that was a superconductor at 90 Kelvin. This was very significant because now it became possible to use liquid nitrogen as the refrigerant. Since these materials superconduct at a significantly higher temperature, they are called High Temperature Superconductors.
Superconductor:-
A substance capable of becoming superconducting at sufficiently low temperatures.A substance in the superconducting state.
Superconductivity:-
It is the phenomena of superconductors at which they are having almost negligible resistance such that the maximum current will flow through them.
THEORY OF SUPERCONDUCTIVITY
A theory of superconductivity is presented, based on the fact that the interaction between electrons resulting from virtual exchange of phonons is attractive when the energy difference between the electrons states involved is less than the phonon energy. It is favorable to form a superconducting phase when this attractive interaction dominates the repulsive screened Coulomb interaction. The normal phase is described by the Bloch individual-particle model. The ground state of a superconductor, formed from a linear combination of normal state configurations in which electrons are virtually excited in pairs of opposite spin and momentum, is lower in energy than the normal state by amount proportional to an average consistent with the isotope effect. A mutually orthogonal set of excited states in one-to-one correspondence with those of the normal phase is obtained by specifying occupation of certain Bloch states and by using the rest to form a linear combination of virtual pair configurations. The theory yields a second-order phase transition and a Meissner effect in the form suggested by Pippard.
DIFFERENT THEORIES OF SUPERCONDUCTIVITY ARE AS FOLLOWING
Phenomenological Theory Superconductivity:
Experimental Facts
Gorter-Casimir Two-Fluid Model
Electrodynamics of Superconductors
Ginzburg-Landau Theory of Superconductivity
Josephson Tunnelling
Influence of Fluctuations
Type-II Superconductors
Microscopic Theory of Superconductivity:
Cooper Instability of Fermi Gas
Self-Consistent Field Method Gor'kov Equations
Linear Response to Magnetic Field
Microscopic Derivation of Ginzburg-Landau Equations
Quasiclassical Approximation
Strong Coupling Theory of Superconductivity
Spin Fluctuations in Superconductors
Triplet Pairing
Theory of Superconducting Alloys:
Influence of Impurities on the Superconducting State
Influence of Correlated Spins on the Critical Temperature Superconductor
Nonmagnetic Localized States in Superconducting Alloys
Kondo Effect in Superconductors
Localization and Superconductivity
Superconductors in a Magnetic Field:
Paramagnetic Effects in Superconductors
Critical Fields of a Superconductor
Superconductivity and Magnetic Order:
Superconductivity and Ferromagnetism
Superconductivity and Antiferromagnetism
Magnetic Structures in Superconductors
Superconductivity in Quasi-One-Dimensional Systems:
Superconductivity and Charge-Density-Waves
Coexistence Between Spin-Density-Waves and Superconductivity
Unconventional Superconductivity:Non-Phononic Mechanisms
Heavy-Fermions Superconductivity
CLASSIFICATIONS OF SUPERCONDUCTIVITY
Superconductors can be classified in accordance with several criteria that depend on our interest in their physical properties, on the understanding we have about them, on how expensive is cooling them or on the material they are made of.
THE CLASSIFICATIONS OF SUPERCONDUCTIVITY IS ON THE BASIS OF:-
By their physical properties
By their critical temperature
By material
By their physical properties :- The physical properties performed for the intermetallics Yb3Co4.3Sn12.7 and Yb3Co4Ge13 crystallizing with the closely related structure types, Yb3Rh4Sn13 and Yb3Co4Ge13. Below Tc = 3.4 K Yb3Co4.3Sn12.7 crosses over into a type-II superconducting ground state with Hc2(0)~2.5 T. Yb3Co4Ge13 stays in the normal state down to 300 mK. The γ value of 2.3(2) mJ gat-1 K-2 and the Debye temperature ΘD = 207(5) K deduced from the specific heat as well as Tc correspond to that of elementary Sn, thus indicating conventional BCS superconductivity.
By their critical temperature:- They can be high temperature generally considered if they reach the superconducting state just cooling them with liquid nitrogen, that is, if Tc > 77 K, or low temperature generally if they need other techniques to be cooled under their critical temperature.
By material:- they can be chemical elements as mercury or lead, alloys as niobium-titanium or germanium-niobium, ceramics as YBCO or the magnesium diboride, or organic superconductors as fullerenes or carbon nanotubes, which technically might be included among the chemical elements as they are made of carbon.
PROPERTIES OF SUPERCONDUCTIVITY
THE PROPERTIES OF SUPERCONDUCTIVITY ARE ON FOLLOWING BASIS:-
1:-ELECTRICAL PROPERTIES\
2:-MAGNETIC PROPERTIES
3:-THERMAL PROPERTIES
4:-LOW TEMPERAURE PROPERTIES
5:-TRANSPORT PROPERTIES
6:-PHYSICAL PROPERTIES
7:-VACUUM PROPERTIES
1:-ELECTRICAL PROPERTIES => Electrical and superconducting properties of rhenium and molybdenum films prepared by electron beam evaporation have been measured as a function of substrate temperature, film thickness, and substrate material. The films were prepared at residual pressures of 5Ã-10^-8 Torr. In addition, films of each material were prepared by reactive deposition at nitrogen pressures in the 10^-5 Torr range. Rhenium films prepared at low residual pressures exhibited superconductivity with onset temperatures from 2.5-4.9 K depending on thickness and substrate temperature.
2:-MAGNETIC PROPERTIES =>
Magnetic properties of tetragonal phases in Nb-Al system have been investigated down to 0.42°K. It has been found that the-phase (Nb2Al) and the intermetallic compound NbAl3 are superconductors with superconducting transition temperature 0.74°K and 0.64°K, respectively. Magnetic susceptibility of the investigated phases does not depend on temperature within the range 4.2°K-300°K, and is equal =(1.0±0.1) Ã- 10-6 emu)/g for Nb2Al, and =(0.9±0.03) Ã- 10-6 emu/g for NbAl3.
3:-THERMAL PROPERTIES => The thermal properties of a superconductor can be compared with those of the same material at the same temperature in the normal state. The material can be forced into the normal state at low temperature by a large enough magnetic field.When a small amount of heat is put into a system, some of the energy is used to increase the lattice vibrations an amount that is the
same for a system in the normal and in the superconducting state, and the remainder is used to increase the energy of the conduction electrons.
4:-LOW TEMPERATURE PROPERTIES => We have investigated the low temperature properties of LuB12 by measuring its magnetic susceptibility, heat capacity, and electrical resistivity, as well as by point-contact spectroscopy using both the spear-anvil type technique and mechanically controllable break junctions. Our specific heat measurements and point contact spectroscopy results indicate that LuB12 is a simple weak-coupling BCS-type superconductor with TC 0.4 K, a superconducting energy gap of 2 0.12 meV, and a very small critical field BC 1 mT. From the dU/dI(U) characteristics in the superconducting state, the energy gap 2, the critical current IC and the Andreev-reflection excess current Iex as a function of normal-state point contact resistance RN have been determined.
5:-TRANSPORT PROPERTIES => Transport properties samples Ba1-xMxFe2As2 M=La and K with a ThCr2Si2-type structure. These samples were systematically characterized by resistivity, thermoelectric power (TEP) and Hall coefficient (RH). BaFe2As2 shows an anomaly in resistivity at about 140 K. The substitution of La for Ba leads to a shift of the anomaly to low temperature, but no superconducting transition is observed. Potassium doping leads to the suppression of the anomaly in resistivity and induces superconductivity at 38 K.
6:-PHYSICAL PROPERTIES => We present studies of the thermal, magnetic, and electrical transport properties of reduced polycrystalline Pr2Ba4Cu7O15−δ (Pr247) showing a superconducting transition at Tc=10-16 K, and compare them with those of as-sintered non-superconducting Pr247. The electrical resistivity in the normal state exhibited T2 dependence up to approximately 150 K. A clear specific heat anomaly was observed at Tc for Pr247 reduced in a vacuum for 24 h, proving the bulk nature of the superconducting state.
7:-VACUUM PROPERTIES => Sputter-deposited thin films of 7 TiZrV are fully activated after 24 h "in situ" heating at 180°C. This activation temperature is the lowest of some 18 different getter coatings studied so far, and it allows the use of the getter thin film technology with aluminium alloy vacuum chambers, which cannot be baked at temperatures higher than 200°C.
HIGH TEMPERATURE SUPERCONDUTIVITY
Temperature above 30 K, which was thought (1960-1980) to be the highest theoretically allowed Tc. The High-temperature superconductors are materials that have a superconducting transition first high-Tc superconductor was discovered in 1986 by Karl Müller and Johannes Bednorz, for which they were awarded the Nobel Prize in Physics in 1987. The term high-temperature superconductor was used interchangeably with cuprate superconductor until Fe-based superconductors were discovered in 2008.High-temperature has three common definitions in the context of superconductivity
Technological applications benefit from both the higher critical temperature being above the boiling point of liquid nitrogen and also the higher critical magnetic field at which superconductivity is destroyed. In magnet applications the high critical magnetic field may be more valuable than the high Tc itself. Some cuprates have an upper critical field around 100 tesla.Cuprate superconductors differ in many important ways from conventional superconductors, such as elemental mercury or lead. There also has been much debate as to high-temperature superconductivity coexisting with magnetic ordering in iron-based superconductors, several ruthenocuprates and other exotic superconductors, and the search continues for other families of materials.The superconductors which allow magnetic fields to penetrate their interior in quantized units of flux, meaning that much higher magnetic fields are required to suppress superconductivity. Their layered structure also affects their response to magnetic fields.
Resistance is a function of temperature:
VISION OF A SUPERCONDUCTING GRID:
Efficiency=>
• Energy sector and transmission losses waste 300 TWh
(equivalent to ~ 400 million barrels of oil) per year
Environment=>
• Superconducting transmission lines require 1/3-1/4 as much
tunneling/trenching as copper
Advantages=>
• No DC resistive losses
• No AC inductive storage - carries only real power, no reactive power
• No AC losses
• Long range transmission of high currents, including undersea
• Very high power ratings including transmission of several GVA
• Fault currents limited by fast acting inverters at AC/DC and DC/AC ends of
the line
• Low voltage transmission, if desired, limiting the need for high voltage
transformers
• Simplified cable design, more amenable to using HTS tape geometry
• Cable coolant also used to cool solid state inverters increasing capacity and
reducing high temperature aging degradation
Disadvantages=>
• Invertors can add substantially to cost
• Most electric power grid infrastructure is AC
Applications=>
Some of the technological applications of superconductivity include :
the production of sensitive magnetometers based on SQUIDs,
fast digital circuits (including those based on Josephson junctions and rapid single flux quantum technology),
powerful superconducting electromagnets used in maglev trains, Magnetic Resonance Imaging (MRI) and Nuclear magnetic resonance (NMR) machines, magnetic confinement fusion reactors and the beam-steering and focusing magnets used in particle accelerators,
low-loss power cables,
RF and microwave filters (e.g., for mobile phone base stations, as well as, military ultra-sensitive/selective receivers),
fast fault current limiters
Railgun and coilgun magnets.
