1. HIGH TEMPERATURE SUPERCONDUCTIVITY 10/30/2015
ANDY HILLIER, STEPHEN GRONOW, BRADLEY REGULA, MATT
DEMATTIE
1
ABSTRACT:
Thisexperimentseekstodrawa relationshipbetweenthe resistivityof superconductingmaterialsand
temperature overtime,asthe superconductorapproachesitscritical temperatureTC.Thiswill be done
by usingtwoDVMATE GPIB devicestomeasure the resistance inthe ceramicsuperconductingyttrium
and bismuthdiscs,aswell asthe thermocouple voltage whichcorrelatestothe temperature of the disc
overtime. The temperature willbe loweredinthe ceramicdiscviacontact with liquidnitrogen. The
voltageswill be recorded withLabVIEWtocreate comma delimitedASCIIcode toconvertintoa
MicrosoftExcel workbook,aswell asto plotthe resistance andthermocouplevoltagestogethersuch
that theyare able tomap the gradual move to zeroresistance atcritical temperature TC and
superconductiveproperties. The Meissnereffectof superconductors will alsobe verified by,ina
stationaryposition,levitatingmagnetsinsituwiththe superconductingmaterial,aswell asnotingthe
critical fieldandcritical currentdensitypropertiesof superconductors.
INTRODUCTION:
ThisexperimentutilizestwoDVMATE GPIB devicestomeasure the resistance of the ceramicdiscatit
approachesitscritical temperature TC,at whichpointithas zeroresistivity.LabVIEWisusedtorecord
the data as comma delimitedASCIIcode,which will be converted intoanexcel workbooksuchthatthe
data isable to be manipulated. Beforethe firstmeasurement,the Meissnereffectisconfirmedby
achievingTC inthe disk,andplacinga magnetoverit,such that itfloatsinplace and it isable to be
rotatedon itsvertical axisbypokingit.
Image depicting Meissner Effect of superconductors. SOURCE: http://www.extremetech.com/wp-content/uploads/2014/08/meissner-effect-superconducting-
levitation-magnet-640x353.jpg

2. HIGH TEMPERATURE SUPERCONDUCTIVITY 10/30/2015
ANDY HILLIER, STEPHEN GRONOW, BRADLEY REGULA, MATT
DEMATTIE
2
THEORY:
Superconductorswere discoverednotlongafterthe turnof the centuryby DutchmanKamerlingh
Ohnnes.Theyare verysignificantbecauseof theirspecial properties.One of thesepropertiesis itsZero
Resistivity.Belowacritical temperature TC,the DCresistivitybecomeszero,allowingclosed
superconductingringstopersistindefinitely. Critical Field,anotherpropertyof superconductors,which
statesthat aftersome certaincritical magneticfieldBC (inthe orderof 10-2
T; the approximate strength
of a small bar magnet),normal resistivityisrestoredtothe material.Thisfieldstrengthof course
dependsonthe material inquestion,anditstemperature. Ina functionof BC/Tx10-2
vs. T/K,the
materialshave the propertiesof normal conductorsabove theirrespectivecurves.Thiscurve hasthe
formB = B0 [1-(T/TC)2
],where B0 isthe fieldatthe temperature zerotemperature limit. The Critical
CurrentDensityrelatesthe magneticfieldproducedbyacurrentin a superconductortoBC: If the fieldB
producedbythe current inthe superconductorexceedsBC,thanthe material returnstonormal
resistivity.The lastrelevantpropertyof superconductorsforthisexperimentisthe Meissnereffect.This
effectshowsthatif an external fieldBEXT (< BC) isappliedtoa superconductor,itwill produce an
opposingcurrenttothisexternal fieldinaccordance withLenz’slaw. Whenamagnetisplacedon top of
a superconductor,then,the currentIis restrictedtoa thinsurface layer,andinside the surface layerthe
effectivefieldiszero(BINT = 0). If BEXT becomesgreaterthanor equal to BC, the Critical Fieldisreached
and will returnthe material toa normal conductor;thisisreferredtoas quenching.The exclusionof
magneticflux forBEXT isnot directlycorrelatedtothe superconductor’szeroresistivity,butratherisa
fundamental propertywhichis very apparentinsuperconductors. There are twotypesof
superconductors,Type IandType II, whichare differentiatedbythe mechanismthroughwhichthey
returnto theirnormal conductingstate whenBEXT becomesgreaterthanBC at a fixedtemperature (less
than the critical temperature).Type Isuperconductorsare characterizedbyasharp transitionwhere the
entiretyof the material becomesnormal almostinstantlywhenitreachesBC;almostall elemental
superconductorsare thistype.Type IIsuperconductorsare characterizedbyagradual returnto normal
properties, notreachingitsnormal resistivitywhenBC isachieved,butgraduallyreturningbacktoit with
increasingBEXT. Thisisnormal in mostalloyandceramic superconductorsthathave a highTC, and is
causedby a ‘mixedstate’inwhichnormal propertiesappearregionallyandincrease withincreasingBEXT.
Superconductivityiscausedbythe lackof electronscatteringinthe material,whichisreflectedinits
zeroresistivityproperty.The Bardeen-CooperSchriefferTheory(BCS),formulatedaround1957, states
that insuperconductors,electrons(±1/2spinFermions) of opposite spinpairupwitheachotherto form
cooperpairswhichessentiallyexhibitthe properties of Bosons.Thisis significant,since Bosonsare not
affectedbythe Pauli ExclusionPrinciple,andthe cooperpairscan thereforoccupythe same energy
state.BelowTC,all of the material’scooperpairsoccupythe groundstate energylevel (Bose-Einstein
condensation).Thisessentiallyallowsall of the cooperpairsinthe material to move freelyacrossthe
material withnochange inenergy,whichmeansnoscatteringisobservedandthe material exhibitszero
resistivity. Cooperpairsformtoachieve a lower energystate (the energyof acooperpairislessthan
that of individual electronsintheirhigherenergystates).The conservationof energythenshowsthat
the energyreleasedthatwasheldbythe electronsbefore theybecame acooperpairisremovedby
conversiontophononsinitsexchange interaction;phononsbeingatype of longitudinal wave. The
exchange interactionshowsthatthe individual electronslose energytoapositive ion,exhibitingvirtual
attraction.Thistheorydoesnotexplainwhy1-2-3materials,though,superconduct.Inthese materials,

3. HIGH TEMPERATURE SUPERCONDUCTIVITY 10/30/2015
ANDY HILLIER, STEPHEN GRONOW, BRADLEY REGULA, MATT
DEMATTIE
3
tunnelingexperimentshave shownthathighTC granulesexhibitsuperconductingpropertiesregionally
inside,butathinsemiconductinglayeroutside. Whilenotheoryexplainsgenerallywhythis
superconductingoccurs,itcan be saidthat the mechanismsthroughwhichitdoesoccurare affected
heavilybystoichiometry,the amountof oxygendeficienciesinthe material’slattice,anditsexposureto
water.Some materialsonlyexhibitsuperconductingincertaincrystal planes.
PROCEDURE:
We hadfirstset upthisexperimentbytakingoursuperconductingdisc (yttrium),andrunningacurrent
throughit usingone of our DVMs. The blackleadsfromthe disc were connectedtoa 500mA current
source,and connectingthe thermocouple wiretothe 5 ½ digitDVMto measure temperature.The
yellowleadsandalligatorclipsare connectedtothe otherDVMto measure the potential dropacross
the sample. AfterturningonourATE, we submergedourdiscinliquidnitrogento bringitdowntoits
critical temperature TC.We had thenverifiedthe Meissnereffectbyplacingasmall rare earthmagnet
on the ceramicdisc andwatchingit float.Toobserve the effectfurther,we hadpokedandproddedthe
magnetto rotate it aroundin place. We had nextusedLabVIEWtorecord the data in 5 runs, afterthe
4th
run usinga bismuthceramicdiscinplace of the yttriumdisc.The savedASCIIcode hadthenbeen
convertedintoacomma delimitedExcel workbook,whichwe manipulatedtoshow our data in the form
of a resistivityvstemperaturegraph,inwhichthe firstX-interceptisthe TC value.
DATA:
-0.0004
-0.0003
-0.0002
-0.0001
0
0.0001
0 0.001 0.002 0.003 0.004 0.005 0.006 0.007
Resistance(mV)
Thermocouple Voltage (mV)
Run 1 (Yttrium)
-0.0004
-0.0003
-0.0002
-0.0001
0
0.0001
0 0.001 0.002 0.003 0.004 0.005 0.006 0.007
Resistance(mV)
Thermocouple Voltage (mV)
Run 2 (Yttrium)

4. HIGH TEMPERATURE SUPERCONDUCTIVITY 10/30/2015
ANDY HILLIER, STEPHEN GRONOW, BRADLEY REGULA, MATT
DEMATTIE
4
-0.0004
-0.0003
-0.0002
-0.0001
0
0.0001
0 0.001 0.002 0.003 0.004 0.005 0.006 0.007
Resistance(mV)
Thermocouple Voltage (mV)
Run 3 (Yttrium)
-0.0005
-0.0004
-0.0003
-0.0002
-0.0001
0
0.0001
0 0.001 0.002 0.003 0.004 0.005 0.006 0.007
Resistance(mV)
Thermocouple Voltage (mV)
Run 4 (Yttrium)
-0.0008
-0.0006
-0.0004
-0.0002
0
0.0002
0 0.001 0.002 0.003 0.004 0.005 0.006 0.007
Resistance(mV)
Thermocouple Voltage (mV)
Run 5 (Bismuth)

5. HIGH TEMPERATURE SUPERCONDUCTIVITY 10/30/2015
ANDY HILLIER, STEPHEN GRONOW, BRADLEY REGULA, MATT
DEMATTIE
5
CONCLUSION/ERROR ANALYSIS:
Thisexperimenthadsoughttodraw a relationshipbetweenthe resistivityof superconductingmaterials
and temperature overtime, asthe superconductorapproached itscritical temperature TC.Thishadbeen
done byusingtwo DVMATE GPIB devicestomeasure the resistance inthe ceramicsuperconducting
yttriumandbismuthdiscs,aswell asthe thermocouple voltage whichcorrelatestothe temperatureof
the disc overtime.The temperature hadbeen loweredinthe ceramicdiscviacontact withliquid
nitrogen.The voltageshadbeen recordedwithLabVIEWtocreate commadelimitedASCIIcode thatwas
converted intoaMicrosoftExcel workbook,aswell asto plotthe resistance andthermocouple voltages
togethersuchthat theywere able tomap the gradual move to zeroresistance atcritical temperature TC
and superconductiveproperties.The Meissnereffectof superconductors alsowas verifiedby,ina
stationaryposition,levitatingmagnetsinsituwiththe superconductingmaterial. The critical fieldand
critical currentdensitypropertiesof superconductorswasalsonoted.The biggestsource of errorinthis
experimentwasthe lackof insulationtocreate a steadiermove toTC.The gradual move toTC was a
reflectionof the coalescingof the superconductinggrainstoallow the free flow of currentwithoutthe
interference of the semiconductive layer,andthe temperature’seffectonthe oxygendeficienciesinthe
lattice.