Table Of ContentPee pagation
Jounal of Seizres Communion
41
100 Years of Superconductivity
Partl
Abstract
Sierconductiigy is w phencmenon of excite zero
law hractane semper fis coovere 9)
Heike’ Kameriingh Onnev in 1941 at Letden in
Water. Like ferrcmaametios and tame specead
fins. superniede is" @ gursan mechanical
phenomenon i maenoscope scale Iris charactenoed by
11) Zero resisiance 6) Pension: Ciopent 2) Perfect
‘homegnetinn d) Hs quanatation ane e) Baer ap.
Sewers necsesgiuattenss were meade since cas
Mts explain te phenornen even Ey pst ie
Btn Heisenberg und Feynman, saat the Theory of
Siverondheti iy yas nacho by Barve, Cooper un
57 ie the US. fn the. nec
mand, conpibcions tows anontanding the
siporeandecthit was mele By Messmer Cchsenfo
London & Lozdon. Fritch Manweil Reynolds ula
oup of Sover phsciis inctting Lacon Gitabun,
Hniosor, rkos, Bogolvubers and ethers. {8
Gather mlevone, the Jasephvow Tmeling, ons
reached ‘Uniden, “becaa of the
egatiment of vers temperate sper
hs eran ereing topic eccasvonay disease in
poster classes, Witt the uiscovery of gh Fr
rcondutoss, Bick eam operate a fig moyen
limporaraes (77 Kj. supercondactiyy 1 nos el
| hin the scope for prectoatapptcaton Even. hit
‘schon stuensseas etpore ad experiment with snow
And inpcrtantrecholoveal eld of plysiee The Part
| ofthis part ait races the ump ide ter he
| tnderstanting of the theory of superconduc from
| BAN io aheue 1982 The second part wil seas the
‘tema of UCN sheory Tope ll supecunductors
\osephson Eee, mgt. sipensendcniy, recent
© deepmens and some applications,
_ Discovery
| The sory of saperoonductvity ean be truce ace to
| tne early 19th esnsary with scientists being able to
uel In 1893. Paraday distovered. that
_tseus chlorine ould be liquefied by 2enerating ist
"ih pressure at one end ofa scaled alass lube and
iWatthe ac end, With a good understanding
ve behind the liquefaction, Faraday sean
to liquey every ‘known gas. is metiod ant
itsuments vere erude, nevertheless, he suceeded
Frqetsing every kina gis, nth tte exceptions
sanygen. nitrogen, and Iydzoger. “nS? French
‘VOLUME 3, NO. 1, JANUARY, 2012
Indranil Sanyat
Physicist Louis # Cailetet,
ind Susy sclentst Rao
Pictot independent y
suecseded in liquety ing
both oxygen end nt
But their yield was se
small” Before that
achieverent. any in the
Fig tele Kamneslingh Seioatifie, community
anes assumed tt those. Bass
lore wis
perhaps
iqueluction, By L883, Karol Olszewski end Zemut
yon Wroblewski in Cricow had sucvected
‘lleting cubic centimeters of liuid wnyen, ard
nilrogen. hn 1862, Tleike Kammerlingh Ones yout
professor af Teiden University, suseccdec, in
developing an apperatis for producing thore in large
(quant ties. The sestem tank aay eaage of what beeae
nown asthe cascade process, The univ wes remains
{o be conquered was hydrogen, as helium as
Uunknewn, although its exisense ia dhe Stn Was
‘own, The liquetacton af mydroges develope toa
bone of eontention between Heike Karserlingh Ones
aw Sir James Dewar, the Seotsh low-ternperat
physicist. 1998, Dewar, succeeced 10 igiety
lhyctogen by taking advantage uf 4 hermdynemie
cffeet know Joule Thomson cxpansion.
7a
Fhg2. Kammering Omes crigina plot ol supercandcting
42
P-. pagation .
Losing the face for Tiguelving hydogen to Devas,
CGanss developed rhs rs helium iguefis i 1908,
nieresirgly, Holium ou d= Fath was discavened
flyin 1935 by the Edalsh chemist Wiliam Rams
Gn taly 10, 908, he sucoessfills Liquefied stium by
vol nst-0 264 dogrees below sero egress Celsius (4
Kelvin or 4 <), The aiseqve'y opened the door to an
etre realm oF passibiity involving law lemperatare
fespetiments. ‘Tus was the fst S.eeesTul allem a
Tigueiyny helium which provided a ne lersperatar
‘approaching absolve zero, Ketmelingh-Oanes
"work a vory low tenperstures just a fe
Alegrees above the absolute ver af temparature. He
sucesedeal in reching temperatures ch co der thas
{yanebefors him and thus opened a new font toe
Science, te eld of fot temperature plsics, Ke snd
covteseutciers Gilles Holst, a stent entrust by
‘Onnes with precise resstaneé measaremenks, nd G.
Flim “he lesbain responsible for the helium
Tiquelter ise, pertinent the experzrens to sluly
wh eppened u aris properics et aerials when
they sere exttemely cok. Helst wis studying the
clscrieal resistance of wires, Te Tound that a he
‘eoled meroary wit, the electsesl cesstance of the
Wie woke an aorupe dtop when he got to abot 3.6
{degrees aboxe absnline es0 The chop ws enorrious
the resistance became et Leas twenty thousand tines
sullen The crop "ook place ove a temperate
interval top smal for theat to measure. As Tar they
fuuld tel, the electrical resistance completly
venished,
Non-superconductive
Metal
“— Superconductor
Resistance
OK Te
Temperature
Fig3.Low te pendant esistne
inNowmal and Soperurctingtsatrals
Previous ests ha founc tat tke resistances fell
texponentilly as the fermperatuce appewacked zero. It
had bees knew far many’ years tthe resistance of
metas fell wien cooled below com sempenasir, but
eas not known what Timing value the resistance
‘would approae’, i the etperiare sere reduced to
‘ery lage to 0K. Some sets, such ae William
in, believed that slechos Rowing. though
conductor would coms tos eompets bal “he
temperature approached. absolute 2er0. Other
Soles, ireluding, Kameringh- Onn, felt that a
Cold wires resistance would dissipate. This sugsen ed
that there would be a steacy decrease in eects
resistance, allowing for better conduction of
lecticiy AL some. very Tow teripersure. point,
Scents fit bat there vu he a leveling ef Bs he
Fsitinee reached some Mile yed anu vaue
Allowing the cuenta flow with fleur esstans
Tinwever. the testing of merery Woke the mation,
‘anes foul ata 423 clgrees Kelvin, the resistance
of mercury fell sharply Lae Kemrlingh-On
Sescibed then enomenonas
At this point somewhat below &.2 KI vtthin some
henareths ofa deere eame aster al not foreseen
by the vibrator theory of resistance tha had Been
framed. bringing the resistances once less than
ion of serial vale atthe msttng po
“Mercury had passed inte anew stat, whichon aevoent
aftsextraordinar elec cal properties may bead
the superconductve state,
Fig (1) shows Oars orca ph presented daring
is Nobel Lecture To expan why resi
depended on emperatine tall Ontes cura
‘tibers Hinstin. recent icv nf quantum
‘ciltors, cevised in 1906 to xplcin the toe
Specie nets of sols Ite etal se
aims ver tat pede the ow oF ent a
‘hese ost ations seca smaller ow fneraue
{5 Einsein wo pode, tea Einsehvsonct nae
might sapin the wey restuncetiminkhed Th
Tul alow temperance Ths pare pruit
“srshetansoa regent asthstonerane
apprnached DK. trover stv of sparc mucl weld
‘ah toward seb. Toto is ace Omer chose
terry. whch could be punfind by din Maton ea
sch tas expested-o hates h yh cooughestoarce
inmevarentai
Repeated trials sonvineed Ques Eat the sudo loss
‘of moreur's resistance a abour 42 K ss eeal The
resul: was Gist presented by Ones al te fs: Solvay
Conterenes, he'd in Brussels from Detar seth 10
November 3d, 1911 under the tile "On the Sedasn
Chanetn she Raroat Which the Resistance of ore
Disappears” He tepurted the work ct hs faborlery
lide: is own rare lene, without co-authors. Holst
ever gor credit for discovering supercondhcts iy.
‘Pe. pagation
“om of Sen Commision
Subsequent fests of in end lead shoved that
Superconductivity was a property of numrous metals
ithhey were covled stent: Figurs(2} ise raph?
fesstnce versus tecaperature is noemal as well as
Superconducting materiel.
By 1914 Ones established a permartent eurent, or
‘what he caed @ “porsisent super ewrenl” in
fpereonduecng coil br ead, The eoil was placed in a
fyosat at ln romperatue, wih the carrer? belie
inlosed hy an este! sakgnelic Feld, Wilh a0
revises, the clectwns in the coil were free to
owt To low indeiritely, In one of Kameengh=
Onnes experiments, he slirted ¢ curmect owing
‘Wop lop ot lend wire cooled ta 4 KA year lor
cient a sil ssi without significant sureent
‘Gas tated that the sale could be destnyed
ily lage magnetic fed wile a
04 loop of supervonductie
ke
supiying s suffice
arent inenced io &
bre persisted for an extraordinarily Teng tite. Le
fkmonsrated the Tavsephosometon by saris
Superconducting current ina ceil ih hs Leiden
Tatoiaery andl dren suspoctiy the oll plas the
retigeraton, which kept it col,
Universiey Tora Tectare demonstration on
Supsreonductivily, Physicists were making
piltr mages to Teen ta observe the conceivable!
Desisteat cuteat in logp of supersarudacting wi
filing with 4 eommen magnet needle,
ve Cambridge
anes report de wot cause much strat that ime, ut
‘Onnes recognized the importante of his discovery 0
the scientific community as well ay its commereal
Pate, An sleevieal conductor with xo resistance
ful cary earcutfa sy distance with a Tasses. I
IisNobel Prize spoech in 1913 (he prize wis awarded
Metals “Transition temperature
Lend (Ph) 196K
Lantus 488K
ic)
Taran a [447K
Mereury (ig) [415K
Tin (Sn) 32K
Indiv tnd 341K
Table I: Superconducting Transition Temperature fae
43
for his tescarshes om bslium), Onnes underlined tre
anexpectec. peuple othe desrese i resistanes,
By 1073, itwes eslaished it the same phenomencn,
naw calecl ihe sipereorudctire stile.” accurred
‘a ad i but Dot gold and platinrn. Ia subsequent
decades other snpereoadveting. metals, alleys and
bompaunds were d scaveved. In 194] sigbiamentride
‘eas found to apr eonlect a6 In 1953 va
silcon displayed supercendieive properties 17.5,
‘in 1962 selena at Westinghouse Coveleped
ies comercial superoorsieting. wire, a slley
hicbium cod ctaniuin NLT. [Tate L shows
Superconducting, Transition Tenperure For some
meals}
Meisxner Effect: The Next Revolution
‘The Flst Work War boough a
temporary. break, in low
temperate research liga
became. unavailable it
Europe. it restated in 1919
‘with gift oF 8 cubie reter
Huliui coming feo the
USA. Teli as abundant
jn the Unived States The
Teiden group resumed wore
bo. sunercanduc-ivity
discovering wnumber of new
Superconducting elements
inline, inven, ete), and
also studying the eaghetic
properties of supesconductos. fu 1923 heliunt was
quefod in Toronto unt J.C. MeLensan. Lo years
er, in 1925, Walther Meissner in Berlin stared
iguid-hetian fener He sis eager te fot One
fgrcupinLsidon, tu Finally onmed Fisww
foaich at Berlin wae remarkable disco
ew classes of supercorslacting slemonts, loys and
then el comps
Fi 4 Waller Meissner
in 1933, Max von Laue, the Gestugn Nobel Laureate,
Suggested to. Meissner” an experinent designed to
Hltermine wheter the cuireat in suereondnesor
Slows on is suiface or in ils bulk. Meissner chose
Soner Oehsonfeld'n cary ou de experiment. other
Suprise they found that'@ superconducting mater
‘epelsamagneti fiend excluces t completely trom
itshull Ths ncasthal sy brat al bar magne
up toa supevcanducte, the superconehcior bends the
Hino of free away tr taal doce alos em £9
penctiat "This phenomendn is known as perfect
lamapoetisny and is today often referred tts the
Meissner effect” and is. very popular demonstration
of supeteonductivity. The Messner fact js 80
strong that a magnet cen uetually. be levitated
44
over a superconductive materia, The Meissner Effet
‘illocer onyitthemagictie eds relanvely sal
Tie magnetic std heecmes tou gre, Hp
the inlror of the metal aude ml foxes is
Suetcuadacuvty THe magnetic fk vanish nth
interor af bulk speci eveu whe ene down
hrtow te munition tperatne ine presence a
magnetic Bei. The iamagrots currents wich flow
inavhin petation layer nee the Surtice of simple
conzected Body to thsi the iene om at
extents applied! ste ae stable nher than
foetescble. Or the or Fand. persistent currents
Towing ia mun eonteted bud eye a lon are
‘1
T<To
TeT¢
FigS Diamagnetc propery efasuperconicte=
An American, FB, Silsse
Leidsn dash,
supe-eende
had suggested (using
iat lhe observed reakdosn of
ityina magnetic Feld wes sullicien 10
explain why supereanducivity. was also. destroyed
Wen the sample carved 2 very lange elects eure
the eurrent sinply created the necessary misanctie
fickl Tue Leiden gevup verified Silsbee’ hypothesis
They slbo developed thesttong caavetion tha, when»
sample became suporeendhcting, whalever magnetic
tax was already aro bssarsefozen in, andl other
‘ehanges in ux through the sample would be excluded
by the perfec: conductivity. Thus the msgnetie state of
the sample was not reversible, 30, thal mo
‘icrnodytaanic analysis could e applied. ‘The result
vvas Wdramitic ane unexpected. vex ‘alien ihe tn
slinders were pot carrying any curren, tie magnetic
Field between thom incfoated hen they were cooled
‘mo their superconducting stare, The fhozeneia fx
‘dea was not corect ard theexclision of applied this
was not nietely 4 dynarvies! effect of perfoe
Enndueriity, Superconductors were not wily perfec
findutors, they were also ‘pericet damages
‘Mathematically, ye obain a particular y ust! Terr
fof thir sult if we Ginie ourselves to. lone
Specimens with long xis parallel to Bsn the
lemougnetizing field contbution to. B willbe
eglisibe, hen
ult BAO cannot he derived trom the
‘thanacterizarion of @ superconductor ac 8 median of
‘zsroresistfvty, From hits as, E=p, ean be easily
Shown that ithe res stivtyp goes zero wile nie
then I mms he vow, By Wlaxwells cy, dBc
proportional ta err F so that aero resistivity pls
wldr0. “This predicts thatthe flax themgh the mal
‘eanrot change n couling through the mastion, The
Meissner et ect conics this reat ard supts
that pe-fectdiamagnetis: is an essential eepery of
the supsreonducting sta
Electrical & Magnetic Properties of
Superconductors
Since shere is no Joss in electrical energy
superconcuctois cany electseal Curent, relatively
harrow ws md of supercorsucting wales ch
bbe used to carry huge currents However, there is
ertin maxinoum coment that there mates cin be
fiuds to cary, ahove ‘whieh they stop hein
Supercaneuctors IF too mien simrent is) pte
tisough a suscreond teri wll revert fo the Hos
slate even thongh it maybe below is transition
‘euperature. The vse of Critical Current Density
(_)t8 4 Tuncton af remperatures tre coker $0U
aperconiuctot the ore current ean “ary
eal applications, J. values in exeess of 100
per scare uillaneter (Aram) are prefered,
AAs closrioe een ins wine eroesamagntic eld
ground a wire, The sicengih of she magilic field
Jeases athe erent in the wre inereases, Recane
Supereendhicrars age able to cary rpe eurcens
‘wnat loss oF enciay ey ane well sited for making
Soong lecromagnots, When a supereondactor 1s
Cooled below its transition temper
Tndgnetic held increased aroun i, the niggnete
Tield remains aroune the supereonducio. Physicists
uke the capital Tener Yas the symbol for Magnetic
Field the rngnetic elds inereased to a given pot
the superconductor will li ornal esinive st
PTT Peee ee eee eeeeee
Pr. pagation
Adour! oS
{he masimurs value Zor the magnetic field ata given
tmpertie is known ae the Creal magnetic fla
and ib given the symbol H. For al supereonductors
‘here exists 8 min of tempecatures and magnetic
Fld within wach the materia i superonsdactng
Oubidethisrepionthematerialisnormal
‘Wher te emperatute is lowered to below the ei
‘emperaiur,(7), the superconduetoe wall “push the
field out of Self. It does this by crating, surface
cen in self which peoduces a magnetic Held
sey countering the etesnal Geld, producing a
"mggneic mivoe", The superconductor becomes
perfsly dtmnagneti canceling ll magnetis ft in
fs intr Thi. pe-Tect_cssnagaetie propery of
Sineronhictors is perhaps the most funeamentl
macroscopic. property al 2 supereanductor Flux
fxclsion du fe what is referred wa the Miisner
fo, canbe easily dernonstated in the classe by
Towering the tenpesatuve of the supersonductor to
below is 7 end placing a Small magnet over i. The
nagaet will bepin to fla: above the superconductor fn
host eases the ini! megnetic Hed From the mag et
ing on the supercoractor will be stron engh
Tint sorte of the field will penetrate the material,
resling. in -mom-supercandacting region. "Tne
ct therefore will net levitse a igh 8 0”
inouced afer the superconductive sate hes bo
chained.
Early Attempts Towards an Explanation
Before iediscovstyof he Meissnereffet,atternpsta
mike theoretical progress. in explaining
$ipetcandit iy, particularly by applying the newly
{seated qusstunttory, aude ie press. Ir real,
therewas ne chance fer anyone to Selve:tispreblem at
thetimeot discovery because before ons could explain
Ione Bats nave the quaatra theory n the form st
Schsktnger md Heisenbers develope. hich did not
Luke place unl the 1920s, Fort long time the
ig. Priteand Tans London
45
nomenon of susewauacivity wes shiraetviced
estalcment that th clselicl resistance vanished
completely AThert Einslein in 1922 cone ued thet
‘Roary wnat yet upto theta
Bonvoen 1928 and 1933 Felix Bloch, whose doctoral
toss in 1928 gave the tnsie theory of conduits i
‘otal, worked onthe problem tages with Wolteaas
Pauli and Lev Laren” Nicls Bohr, Nemer Hester
saul Leon Hriloin also jomned the oH, but thot
The discovery of the Meisner Freel was 1 eucl
turning pon. Supcrcorductivity ull coud ol be
sxplained it tom of quentam mechanics, bot the
thermodynamics of the phenomenon was
tinlertandele Pan Fhvenfest who believed tat
Teswomunivy God pe teed sae me anes
‘scnmaon tt ernsuet le ar
Bsa mice (ses eyed Conc Ge 9
Salen ct ee Ht iia
rm lacs coms poe to ous we
Rend toy evay tone Cor wel Got
ahead to ful oly eco tC aber
eu tei puss naiion at ans a
‘SStmnnmic fpr post th
cr ar ee rd stat te
crpennt PD fers a facton i of he
Seaton cal fa Gebel haag coke Boe
SSperd” whch i pay esque er te
rsmcabie perso seconds le
FBovcuay cocoon osetia ca
erations The un Bp, es weal
Som zo Toto nig TO, whee al ot tie
ether sein esmpetl condensate
[A seeond inode themes wlvanse came i de
following yea, when bothers riz and Hats Lona,
oo efvgees dum Nasi Germany, atthe Clarendon
[aborts at Oxford, propose ther phenomenal
theory of the electomagneticy properties of
superconductor, in whieh the diamagnetic rather tha
flere pecs wore ussursel te Bemors funda. In
fn olny metal we dere the shenemenen of
loecal resistance by the fous Ohm's law. What the
Tol bras cid wats fo shew tht thre ws annthar
rhamatealrelsioship which shouldbe od in plsse
fof Ome Law to serie superconductors, Trot this
‘other eltonship waich they developed. they ware able
tw explain hth the Mrissne-Ccer fel expen
swell atthe persitonrcun to Kareingh-Cnns as 60
roanifstations ofthese sthin,
‘They sugaestsd thatthe eloctricalovrent density j
curred by tie suport isteated tothe cleric Held E
46
P< pagation
and magnetic field Rat ech point in epace by two
TLondan equations expressed in forms of measurable
fells
a,
ot om
Hore 4, the superconducting current, Hane B are
respective the lest and maghetie Fie with the
Supercond cores the charge of unelectron& proto,
nivis election mass, and N, Is a phenemenslogical
Chrstant loosely asneiated With @ Humber density of
Superonndueting crsers,
ne . ne
F
“The Pvo equations ean be samhined to farm a single
“London auation” in tam of the magnetic yeclor
potena AV
A is ta be chosen suck the V0 wo ensure current
‘Sonsevation, Ifthe socond of London's squntions is
‘anipulated by applying Ampere’ aw
aj
VxB=>
‘hen theresultis the ditferentil equation
iB 2k (es
ann,e
VB
“Therefare Rs) Bye
“Thus, the Tondon equations imply a chanscterstie
lerath Seale over whieh external magreti elds are
‘xponenticiy "suppressed. This value athe Landon
pee ph ha tat a rage el
Gisunce which sooner of 10" ce in typcal
Superconductors for well below T, Observed vas
“otfearehoweversevera imesthe Lénon val.
Front Londor: theory the iiportane phennmrena of ux
fqurization cay be sauly understood. We corset
HceaStpereonduingeng. espn helo aie
Supcteometor the is compleeey
Sekced cut, th “heros, super currents should be
absent there he
fintt~0
Inrodocing super eutentdeasity and reartanging we
. faat [fas bs
ig themagneti Ane throgh the rng, We see Sen, that
themanee xc isquanited
2mhe
#02 nbs
inumtsofthe Mux quantum: ==
ee
candensation ofthe average moments dstibution”
Development Between 1950-57
‘The Second Werle War interrupted research in
supercencuctvity just as the First, World, Wor had
Sone. It wes aot uh sbout 1950 tat real progress
began ones again to be made, The phenomenc cil
resisted ary tue microscopic understanding, ut some
hicces of the purzle did heuin to caste (ogelhes,
perioulary mn the phenomenological model of Vitaly
Ginsburg and Lev Landau. Ginzburg and Landay
(1950) extended the London plenomenolagy int
Priliat stroke based en Landat’s theory of seocad
agation
Alsi of Save Commision
SERRE EREEEE EERE ERE EE ES
47
nlerphase reasons. does not pupert to expan
the iMictescupie. mechanisms BIving. niet
fupetconductiity. Ingtsady ic exeiines. the
Inatesepiepropenics of «superzantor with the
hid gata hernacsmnio argument Ths theory
insometies eal ed phemomerolngie” sit deseribcs
sonco the pheroneta of superset iy thot
‘Aplaning che nersing eerscopic mectanisr
Buse on Landauspzeviouls-etanishod theory of
secomurder piso tansians, Landa and Ging.ua
Iated that he ow energy Fo asipereondcoc at
ie stpercondicing Wauiion cat Bs expressed
tsa eamps ocr pst hich Gesrbes
dow deep int hespetcadicing prose rhe syste.
The foe enety hat the form we Fi the ive
np
cit -zeay| lO
=
ole Slot a5
energy inthe rommal phase. @ and ff are
pientmenologieal pacameters mis an effective miss,
isthe chage of an elects, A isthe magnetic vector
pots and Bouck is The imagnete field. By
he fee eneruy with respect o fluctuations
Parameter and the veetor poten, ae
evesatthe Ginsburg. Landau equations
a + BIPPY + 3b (ihV-20Ay¥—0
we (ifV - 2eA)y}
where j denotes the eleetcal suront density and Re
the real pari. Tho first equalien, which Deals
inercstingsimilarives te the time-independent
uation, determines the order paraaseler
‘applied magnetis field. The second
thes prosides [ie spetconductin
Equation
futon Thistheory ws ners by Geko 105)
tb hea limiting ease of tie BCS tauey and remains
today ashe standne initial appoach to pubes wit
spills varying superconducting stats, The veel
sipfizance ofthe wavs functioliks order parameter
‘vould net be explained until the microscopic BCS
theory came along towa'ds the end of the decade
However even aller the BCS theory provided a
Iniemstopic understanding of supereoaduedvily, th
‘much simpler id easiero-ase Gincburg-Landsa
moti remained (and remains) the every-day working
hoory used by theorist and experimertalsts ale t0
snaly7> all manner of eamplex phewmena in
superconducti
rm]
Fig? Wiely Gincburp(le®bondLoy Landa
Annimportant concent wae rtrudcedby A.B. Pippard
fin 1983. Aided by watlime development in high
{recuency technclogy. Pippurd was abe to sake very
precise msesuromenis of ho compare with London
Eqcation, using parameters determined fo. similar
measurements of th skit dept the normal state
metals Fe toond tha, event =U, the hited value of
yeas less than the desty of corduston elec on
the aomal sate, by'a ratio a was arger “oel0%
spaterialslikeal (7= 1K} han fo: metals like P(e
7K), He concluded that « "cohersnee Kong” is
‘sociated wit) the superconducting state ich Chat a
pertushetion of the superoenductor ata. point
Decessily influences the superthuidwihin adistence
2,0" thatpoine For pure etal, 3-10" ct. for T=
Tle generalized the Londor. equation to & abn-luedl
forct nl accounted fer thetuct that cho experimental
‘alue of *he penetration depth is sveral times lager
han the “London yalue.” Suosequemty. Barusen
sued that Pippares aop-loel rstion Would likely
follow fromancnrgy gp mee
Perhaps the single most iesportant experiment wish
directly played wriding role to an explastion of
Supereonactiviry sens the experiment onthe "sot
tffect" This oocured in tha spring 0f 1980, Pa
fom ta taboratories simaltaneotsly reveal he
same result One paper avis bv Reynoles, Seri
Wight and Nesbitt at Rutgers Liniversly. The whet
vsas by F- Maxwell at the U.S. Nasional Bureau of |
Standards. Roth groups measured the ansison
leamperatures of separated mercury sotopss and
that in meteor yT, wares fin 4,156 toe 40K a the
average atomic mass M varies Tn! 195 (0 2034
‘42m. The tansition temperature changes staoethly a>
tfffrentsotapes ofa same element mined Tis reult
behavastarie elation: M'T.=Constant
‘Sultans rn
ca azs007
He SDH 08
Pb 9.0 02 |
Zn 045.005
Ze one.08 :
Tile 2 Observed alucs oF
Tor isaupe ele
Soperoondustors
48
Ir; pagation
From the above relation and data between T, ans)
snipe mass, wean understand tat Jatice vibiation
td slecinnla tice aration ace elewely vlad bo
Superconcuctvity So wt the Hsolopie experiments
ta talked abun showed otha although the
lscreal conductivity was known te arse because of
{he moson ofthe elecizons, there's some ale of these
Ince vitwaions ‘They enable the eloctrans snddenty
1 move through the lates, evidently without
Irind-ance, when che sample Ts cooled tothe critical
superconducting temperature.
asthe elementary discovery thar transition
temperature depends an murnher of neleons. the mass
bro lanes imporsat, het mesian and ts the aie:
Vibrations mint he fie. Independent, Brisk
physicist Herbert Prhlich, sso was thon spending the
Eprny term sf Pardue University, aorpedtn develop
theory of superconductivity taned onthe self enero
{Melgctnsin the Reldot phonon. He aed abou! the
isotepeeffct in mite May choy before he sented
his paper fox publication aid was clighed to find very
sir experimentl canfirmation of is ideas He used
Tanatosian, nat called the Fblien Hamma,
‘shich interactions between loetons and phonons ae
Jcluded but Ceulomp intractensaromifed excest as
bey’ cm be included inthe enezges ofthe individual
flecross and phonons, Froalien used a perarstion
theory approach an fouud iusisbility ut dhe Pets
Surface the. clacton pronon inferaetion were
Sufciemy strong, Herbert Iblieh realized thatthe
‘bservation that-goed conductors (capper, gold) tend
hot to Geoome sirereundacior might ean that
fnperconduetvity is proctied hy 4 relatively some,
inferation between the conduction elections and the
Tntice vitrtions, or honons, in those metals thx were
not goed nontal conductors,
“The nent big experimental discovery wps dane by 10
groups: Goodin, who was making thermal
tonduetivity experimen, and Brown, Zemansky ard
[Doorse, who were making spee:ficheatmeasuremens.
They dcuvered wll isealed liceosrey gap.
T % 7
Figs. Temperature veraon of elesronie spite heat of
onal tl eestor
“The specific Heat af w solid C, vat be expresses
= YE tay whote the frst tem is the electron
‘dntrdution (predominant for poo! meals at very foe
feruperture) an the sce tennis. the. La
Contribution, The graph hove ft shows the savior
‘of none? mil vile tha ia the right shows
‘behavior inthe superconducting sae. The saris
featurcorthe cura thar below Ts the false 982
indicating 9 cleat gap in the. slecrtnie. enemy
speculum Tie possible nen eves for elecvas ree
{w move. about a. volume. V_are found om, the
Sehvingerecuation. Theeacmy levels are quantize
find each level (2) ean be peer psd by twa “ermions
‘ane th spin up ane one with spin dwn. ACT 0. the
fnorgy leve's Will be copletely Billed up wo a cenain
‘is whe is called she Fermi eneseysc,-AtT ~0,
thon willbe tonceupiedstatorvith ea, Inmetalsin
‘aval sate, eleettens move above the Ferms kneray
INT 0K. Hutin speroordeetingstete tht ienot ey
you ond to impat sufficiently more euensy
fxevenme an enerey gan ahove the Fermi Fnerey.
‘yas a sial clue towards cmccing. the theory oF
superconductris
‘Thos dy 1959-56, t90 inications were clear the
leetton phonon interseion and energy gap. Ll
fumpteheusive theory was sill euging seienssts
Memhile, Schatroth showed that stat ne with the
Frallieh THamilonicn, sone earnet decive the
Messner eTect in any order of perturbation theory
Rassien poste” Migdalsthoory supposedly eorect
{terns oforder mM)" gave no papa nsf at
the Temi surlace aad no Indication of
-Wob Sebuioter suramarizo she situation as “This was
he state of ow tndvstandng of the etectodsaamtes
(felsic eyecare mss 98a ters
Satisfactory phenomenaloay, Ino “explanation” on
Intervccepie terms. What was the rare of the
Impertondioting siake hat made i have these
remarkasleproperies? This question was antiered by
‘ne sake by the lassie piper of Randeon, Cope
ona Sehrietiee (1957).
Events Leading to the BCS Theory
The ann whos pat breaking esc eatin
Satisfactory explanation tw the. pasnonsenon of
Supotconduetivity was John Bardeen. Burdasn reals
that "My fest inmoduetion 10 superconducthaty cane
ihe 1930 and greatly potted fron reading Daal
Shccnbere’s ite Bock on sapercometinty shih
avons excellent summary ef he experimental ings
dit of the phenntonoligical theries Oat foal Deen
flevefoped* Radcen's fist abortive “atempt t
*P. pagation
Alf Senos Conmaication
49
onsruta theory, 940, was stonglyintaenved by
Londons ideas an the key ices was sal mre 2a
athe Femi surface ariing. om smal lihice
Fixplaeren's. However this Wek eas inemapsec By
several yeursofwsrtime research, al then tee wt
Hacdeen joined the wroup at the Tell “Tlephone
Laboratoses hers his wore tured fe semicon tors
ardeen cane o University of Minos at Urhanain the
early T9593 as jointly a professor of physics and ¢
profesor of elstineal engiteermg at ‘he fom Bell
Ltbmatores waere ho, Walter rata, aad Wa
Shockley uneated he ansistorfewae not unl the as
a resul of the discovery o” te tsotope ell tha
Eandeen aguin hogan to. eccnieiterested th
Sipsreonducivine Haneen teard aout the isotope
effect invarly Nx, 1980 in telephone ell fem Seen
fd realized that the jcotose effect identified the
lnteratot beeen clectres and phos thet mst be
response fr the henocrenon. The basic ea wr
beu Fenmi degenerare gas oF neuly foe electrons wil
a sakly attactiv> interaction by way of the atioe
Ponons, he atreed fo wevive his ead tory of
nergy gaps atthe Fermi surluce, wth the aps Row
atising four dsnamie Interactions with the phonons
father thax ifom sill sate lance cispagemetts
Baricen wed a variational metal tier than
peturbacionappragch but tae thcory ay alse based et
the elvtnn sel-cnenpy in ho fit of ponooy Al he
same tine, Bardeen rad Frohlich tndependenty put
fvand theories of superuomcrvity whieh late on
treats nso cams cident at ey
allofth selFenergy is included inthe sural state ne!
isbinle changed inthe wansiti. A theory aaving
trie many-body mteraetion herween he clecttens
seeredi0 2 eyuired to aeeuene Ft superent Ay
Howovs., sah oF thew sad they thought an essential
Postion of he problem Tal wo coat what happened 12
tho eleticons whose energy was wal to the Fett
fang. The interaction sided by’ Fright af Fist
Sich quite spacalis be ne both novel and pont
involving tte right dependence on the iotapie mun
‘Phere wos however a ngjor ratte in anderstandiag
fw it could play a role, since the baie Cavlarnb
ineraction between electrons s both fepulive and very
mack stronger, “AS Lande pur i've ron repeat!
Couonstav
In 195, stituted by writing a review antile om the
stu the theory of superconducivity, Jam Boren
sided to renew the alla om the pioblem, Solving
ltarprolemprovedtobe dificult tisk There wa he
the sr af power competition, Richard Fey nts,
tne ofthe masters of quinn sletredynamics, an
fenowned Soviet Physivists like Landa and
ego yubor were close ta th solution. In quantum
jerbdynamiss clecuons in vacua interact With one
‘other via photons, or qaumtizd light weaves, fa the
Proce! Bardeen ws cy-nu tool, ¢ etronsin meals
interact with ome arother via phedees, ur guantized
lewive vibsations, This seas the problem which Soli
Bardeen and David Pines, his postdoc fellow a the
University of Illinois during the peti 1959:
stacked, What they fosnd fy extending an appre
‘whieh David Bahn ane. David Pines had carlice
developed or understasling the cor sequences oF
rox-clectrom interactions in rita, ras that he
meclunn is the messege, When “hey tous into account
the influence of electronic sereering processes on at
tlectromelectrun and election ineraetien, the
Feud thatthe presence of a second commer the
makes possible’ a net attractive. interact on
hapa of elostons whe energy eilerence 1
than acharcctvistc phonon snerey
Fig 9 Baier (let, Cooper (enter) and Scher
In 1955, when Pines tefl University of Enis,
Brdden decided dat reinforce ets vere needed I
called up CN. Yang at the Testute for Advenced
smdy a Princeton, to ask for 2 posidae vers i he
Field theory. Vane reromsmended sun Cooper snes
Cooper's fickground was 1 pasiele physiet Cooper
has recently completed hisPhD in garicle physvs
in the process he ad leamed set of mathematical
lechniquescalled quantum “eldtheory. He wasted
fasone ofthe best young sen inthe subject. Bande
Fete migit be imporantw knovr these ‘echn ques in
order tickle the problem af superoonductiy. So ie
a
Fig, 10, Sehemasic repesentaion of Comper Pa
50
wited Couper to come w Urbana, Because of is
ssery in quantum mechanics Ke was jekingly called
by otters in the depertneat as “Bardeen quantune
imeckanie". Meanwhile, Bob Schrier was tthe
University of Hinois a6 a graduate studeat, He had
er henna states at MIT, woking
ina group of sai state physicists When he reas
tradition time. he deciced ty work with Ranieen
Initislly, Rardesn supgested “scma. ware on
scininviustrs When came time tiv 2 resis,
ier chase to woek an superenndietivity The
team was astomnbled at the University nf Hlinsis
phhyses depanmiont, Banteen and Caper hc za shane
naffice Intherrcantime, Schrieffer wankesinaroam
fl of exher grants stadonts The stution was aot
conducive, butspiritofteteiowas on high
+ son howame els that snes the existing field
thooretie methods were hasce on perturbation tsar,
snoter seme woul ae t be devsed. Breen
Stressed the importance of an ene-gy” gp the
fexeitatin spectrum and thar suporeondtetiviy cle
‘0 eandensatin in momentum space af 4 coherent
‘Superposition oF narmal-sate configurations. But It
‘as ficult ro explain quantiatively. Farunstely,
Tanda's ‘hony of a Fett liquid) voviled
jeeessary, basis Ter" Geating the normal-state
xciations in onc-le-one eomtspondenee with “he
ites electyn gas 0 that he small condensation energy
hoswoon thesuperand norinal phases could he slate
The fist, major beeakshcough this tio made. in
superwancductiviy came fom Leen Coaper. Coopet
‘vas making an efor fo find out why’ thero was an
agation
A varal f Stines Commectin
‘enerey gap. Cooper studied the genera theories of
‘Guat ‘tiechanies and considered simpliticd
adel ates interactions of ewoctcctznns At very fa
‘emperatore, ll sates upto Fermi level ar filled snd
hanes. no available th these clecrons. He. then
{Seaminad what considersd = the fis sis that the
‘Coutsmb repulsion of elevtrans, because they are of
the same shure, The second was thi the electrons
interact ia lattice vibrations: one eleston displaces 3
hielsis ar i pastes by tho maolous which sn hin
[tracts another electron forming a pair of moving
Glectons, Ihe interaction Was energetically forse
“thers was net atracion,
Cooper sonluded that supercondactvny arose when
theetiveinemeton of neler ferns other
Trorgh the ates, wa lange ta tse ied
epulsion This then hocume a “ererion tor
Sipercemeliiy Cone pablsiels pape in 1956
finds une othe famou papers Ihe history ob
ipesconductiviy The incerasting pas cf elects
ihave since been known ax "Cooper air er the
Ginooverr. es imorosing to ote thts is 198
papa Canpsrretored to Citabury and Seater a+
Enbing thao electrons or even mis, omnes
together andl zero or ttegal spin ould bebe
IikeBosons
this point Bardeen, Cooper and Sehr decides to
lay > gensalize Coopers tsils {0 many elsctor
Sens The ouble wes that a Cooper Pair pease
Uo crt wilh hil Rua lscow waft
‘They ndertoad th sivele Cooper ir No
usgble The break came. when sb. Sclrieer
Succeeded in guesing the natire of te ston ak
sects aor ‘Tey them stenpted la generalize te
Salons the higher temperatres and shew thst
Fens ‘cold neu rll of the et
Sperconevctiity, The ftv! jeint-piper of he
rupwas published ia Febauay, 1957 Mis was the
prolif ratory
The tio then fle they were close fo the success Bat
they st had fais Berdcen none to Stckhaies n
tollest bis 1986. Nobel Pave while Cocper and
Scnricnor ongrosced ints. deep thineing and
faleulaon, Tut wilsia few malts they” were
Successful. Te became leer that ths "Roy 10
Supercunductviy isthe vandessaliva of all eletuon
pales inga-montehgunt speed, hat Is they will have
me moraenton {though thoy’ may be pyseal Tar
Spatt) anda be described by ering e wars hac
Tis easy to understand thet such situation nay arse
asthe Cooper Pairsare Bosors andar not stricted be
Paull Exclusion Prinepie wo oecupy same enerzy
2
3
2
2
a
