2. • What is Superconductor?Or What is Superconductivity?
• A superconductor is a material that loses all its resistance to the flowof electric current whenit is cooled below
a certaintemperature called the critical temperature Tc. Example:Hg, Zn, Nb.
• Superconductivityis a phenomenon in whichcertainmetals, alloys and ceramics conduct electricitywithout
resistance whenit is cooled belowa certaintemperature called the critical temperature Tc.
• What is Critical Temperature?
• The temperature at whicha material’selectrical resistivitydrops to absolutezero is called the critical
temperature or transition temperature Tc.
• What is Critical Temperature?Explain usingresistivityversus temperature plot.
• The temperature at whicha material’selectrical resistivitydrops to absolutezero is called the critical
temperature or transition temperature Tc.
3. Fromfigure it can be seenthat the electricalresistivityof normal
metal decreases steadilyas the temperature is decreasedand reaches
a low value at 0K called the residual resistivityρ0. But in contrast, the
electrical resistivityof mercurysuddenlydropsto zero at critical
temperature Tc and is 4.2 K for Hg.
4. • Discuss various properties of Superconductor.
• Few important properties of superconductors are as follows:
• Electrical resistance
• The electrical resistance of a superconducting material is very low.
• Effectof impurities
• When impurities are added to superconducting elements, the superconducting propertyis not
lost, but the Tc value is lowered.
• Isotope effects
5. • ThecriticalortransitiontemperatureTc valueofa superconductoris foundtovarywithitsisotopicmass.Thisvariationin Tcwithits isotopicmassis calledtheisotopiceffect.
• The relation betweenTc and the isotopicmassis given by
• Tc ∝
𝟏
𝑴
whereM is theisotopicmass
• Magneticfieldeffect
• Theminimummagneticfieldrequiredto destroythesuperconductingstateis calledthecriticalmagneticfield Hc.Thecriticalmagneticfieldof a superconductoris a functionof temperature.
• Criticalcurrent densityJc and criticalcurrent Ic
• Thecriticalcurrentdensitycanbe definedasthe maximumcurrentthatcanbe permittedina superconductingmaterialwithoutdestroyingitssuperconductivitystate.
• TherelationbetweenIc andHc
• Ic = 2𝝅𝒓 Hc
• TherelationbetweenIcandJc
• Jc =
𝐈 𝒄
𝑨
Ais superconductingspecimen’scross-sectionalarea.
• Persistent current
• Thissteadyflowof currentina superconductingringwithoutanypotentialderivingit is calledthepersistentcurrent.
• Meissnereffect(Diamagneticproperty) Thecompleteexpulsionof allthemagneticfieldbya
superconductingmaterialis calledthe‘Meissnereffect’.
7. The above processoccursdue to the development of surface current,
which in turnresultsin the development of magnetization M withinthe
superconducting material.Hence,as the developed magnitationand
the appliedfieldare equalin magnitude butopposite in direction,they
canceleachothereverywhere inside the material.Thus,belowTc a
superconductor is a perfectlydiamagneticsubstance
(𝛘m = -1).
To prove 𝛘m= -1 for superconductors
We knowthat induction or magneticfluxintensityis givenby,
B = µ0 (M+ H)
........ (1)
Where
µ0is the permeabilityof free space
M is theintensityof magnetisation
and
H is the appliedmagneticfield.
But,for superconductorB = 0
8. • Therefore,Equation(1)canbe writtenas
• 0 = µ0 (M + H)
• ∵ µ0 ≠ 𝟎
• M + H = 0
• or M = - H
• or
𝑴
𝑯
= −𝟏
• Hence, 𝛘m = -1 where 𝛘m =
𝑴
𝑯
iscalledthemagneticsusceptibility.
• Provethatforsuperconductors,magneticsusceptibilityis -1.
• Weknowthatinductionormagneticfluxintensityis givenby,
• B= µ0 (M + H) ........(1)
• Where µ0is thepermeabilityoffreespace
• M is theintensityofmagnetisation
• and H is theappliedmagneticfield.
• But,forsuperconductorB = 0
• Therefore,Equation(1)canbe writtenas
• 0 = µ0 (M + H)
• ∵ µ0 ≠ 𝟎
• M + H = 0
9. Type I superconductors Type II superconductors
These superconductors are called soft
superconductors.
These superconductors are called hard
superconductors.
Only one critical field exists for these
superconductors.
Two critical fields Hc1(Lower critical field) and
Hc2(Upper critical field) exist for these superconductors
or M = - H
or MH=-1
Hence, 𝛘m = -1 where 𝛘m = MH is calledthemagneticsusceptibility.
• Discusstypesof Superconductors
•Basedon their behaviourin appliedmagneticfieldsuperconductorsare classifiedintotwo types:
•Type I superconductors:Type I superconductorsare thosewhichexhibitcompleteMeissnereffect,i.e., theyare completelydiamagnetic. They are alsocalledsoft
superconductors.
Example: Pb, Hg, Sn.
•Type II superconductors:Type II superconductorsare thosewhichdo notexhibitcompleteMeissnereffect. They are alsocalledhardsuperconductors.
Example:Y1Ba2Cu3O7, Nb3Sn, Nb3Ge.
•Basedon thecoolantsto achievesuperconductingstatein a material, theyfallintotwocategories:
•Low-temperaturesuperconductors:Superconductorsthatuse liquidheliumas coolantarecalledLow-temperaturesuperconductors.
•High-temperaturesuperconductors:Superconductorsthatuse nitrogenas coolantare calledHigh-temperaturesuperconductors.
• Whatis thedifference betweenType - I and Type – II superconductors?
10. • Explain Low and High temperature superconductors.
•Low-temperature superconductors: Superconductors that use liquid helium as coolant are calle
Low-temperature superconductors.
•High-temperature superconductors: Superconductors that use nitrogen as coolant are called H
temperature superconductors.
• Draw structure of YBCO superconductor.
11. • Write applications of Superconductors
• The application of superconductors are as follows:
• Superconductors can be used to transmit electrical power over very long distances without any power loss or any voltage drop.
• Superconducting generators has the benefit of small size and low energy consumption than the conventional generators.
• Ore separation can be done efficiently using superconducting magnets.
• Very fast and accurate computers can be constructed using superconducting magnets.
• Very strong magnetic fields can be generated with coils made of high Tc superconducting materials.
• Superconductors can act as relay or switching system in a computer. They can be used as a memory or storage element in computers.
• Superconducting device can be used to detect by small magnetic field changes.
• What is the basicprincipleused in the magneticlevitation.
• The basic principle for achieving magnetic levitation is as follows:
• Zero resistance
• Meissner effect
• ExplainJosephsonjunctionusing schematic diagram.
• A Josephson junction is a junction formed with two superconductors with a very thin strip of an insulator separating them. Josephson junctions are used in sensitive
magnetometers called SQUID- Superconducting Quantum Interference Device. A SQUID is formed by connecting two Josephson junctions in parallel.
