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Superconducting Point Contacts Weakly Connecting Two Superconductors and Electrostatic Effects in Superconductors Due to Temperature Gradients

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Superconducting Point Contacts Weakly Connecting Two Superconductors and Electrostatic Effects in Superconductors Due to Temperature Gradients SUPERCONDUCTING POINT CONTACTS WEAKLY CONNECTING TWO SUPERCONDUCTORS AND ELECTROSTATIC EFFECTS IN SUPERCONDUCTORS DUE TO TEMPERATURE GRADIENTS A. TH. A. M. DE WAELE ms E R R A T A, A.Th.A.M. de Waele, Thesis p. 26 The captions to the figures 6 and 7 should be interchanged. P. 32 In the last formula there has to be an equality sign between the two last fractions. p. 77 The second line of eq,(6.') should read = - Vjri4 - m.VH = - W° p + sVT + -p -42 7 v vn - vs y' - in4 VH (6.1) p. 78 On this page m s m = electron mass. The second line of the first formula should reads =: - V2\i + 2e(E + v x B) - 2m VH OQ 3* sr o H- 0Q CL> en » n ro ro 3 ro 01 01 C rt rt rt 8. ro 9 9 Cf 01 11 H3* c I-h m rt M» OQ 0) o ro H- g a ro ro ro ro ro ce i-> rt 0Q O ro !-• H- < ro n ro N T3 01 9 C ^ n> ro c o 3 rt O 3 rt ro n> tr. C o rt rt 11 o 01 a O- OQ O. OQ 9 M ro M ro o rs 01 ro CA H- 01 rt cr 01 cr- O • ro 9 ON a to 3" cr rt O 01 c M rt < er rf H» ro ro H- 3 03 n> * 3" 3 i—' 9 rt OQ 01 OQ g •13 3Q ta ro rort g rt O o. 3* o oIt rt H- O a rt rt ro § cr O C CL ro ro 01 o 9 a (A H- rt ro ro » ro s STELLINGEN Vant-Hull, Simpkins en Harding hebben de magnetísche ruis van een staaf normaal metaal gemeten door de staaf in de holte van een dubbelpuntcontact te schuiven. Bij de interpretatie van de uitkomsten van deze meting dient de invloed van dit normale metaal op de werking van het dubbelpuntcontact te worden betrokken. L. Vant-Hull, R.A. Simpkins and J.T. Harding Phys. Lett. 24, 736 (1967) Dit proefschrift §4.6. II <u De alternatieve verklaring die Gubankov, Likharev en Margolin c\j geven voor de gemeten i als functie van B± , die wordt beschreven in figuur 16 van dit proefschrift, leidt niet tot bevredigende overeenstemming tussen de gemeten en de berekende waarden. De zelf- inductie van het omsloten oppervlak van het dubbelpuntcontact mag derhalve niet worden verwaarloosd. V.N. Gubankov, K.K. Likharev and N.M. Margolin, Sov. Phys.-Solid State 14, 819 (1972). CM III 4- Het gebrek aan overeenstemming tussen de théorie, die Mercereau OJ vocr een dubbele Dayem-brug heeft ontwikkeli, en het experiment, is ro het gevolg van een foutieve beschrijving van het systeem en niet van het feit dat in de théorie thermische ruis buiten beschouwing werd geläten. J.E. Mercereau, Rev. de Phys. Appl. (Paris) 5, 13 (1970). IV De verklaring van het verdwijnen van het ,,patch-effect" bij L)e druk in de vloeibaar-helium temperaturen wordt gezocht in de invloed die een superfluïde compone geadsorbeerd laagje kan hebben op de uittreepotentiaal van verschil- toestand gelijk aar lende kristaloppervlakken van een metaal. Deze verklaring kan worden V.M. Kont get-oetst door gebruik te maken van experimentele technieken die in D.L. Good deel II van dit proefschrift zijn beschreven. 447 (197)1 F.C. Witteborn and W.M. Fairbank, Nature 220, 436 (1968). Voor het meten domeingrootte in de behulp van neutrone In verband met de mogelijkheid om op eenvoudige wijze läge tem- gelet op de beschik peraturen te bereiken, is het van belang de thermische effecten te een golflengte van bestude. °n die gepaard gaan met veldemissie van electronen. VI In verband met de théorie van Misner dat de gravitatiestraling Het besturen v die door Weber is waargenomen het gevolg is van ^ravitatie- multidisciplinair t synchrotron straling, verdient het aanbeveling ook de polarisatie Dit leidt voor de n van de gravitatiestraling te meten. meerderheid van de C.W. Misner, Phys. Rev. Lett. 28, 994 (1972). die maar zeer ten d kan worden verbeter VII Het argument waarmee Einstein de algemene geldigheid van de A.Th.A.M. de Waele door hem ontwikkelde théorie over gravitatiestraling in twijfel trekc is niet steekhoudend. A. Einstein, Sitzungsberichte der Preussischen Akademie der Wissenschaften, Berlin, 154 (1918). VIII van het ,,patch-effect" bij De. druk in de damp juist buiten een heliumfilm, waarin de in de invloed die een superfluïde component al dan niet beweegt, is in een stationaire epotentiaal van verschil- toes tand gelijk aan de verzadigde dampdruk. eze verklaring kan worden V.M. Kontorovich, Sov. Phys. JETP j}» 770 (1956). ntele technieken die in D.L. Goodstein and P.G. Saffman, Proc. R. Soc. A 325, i. 447 (1971). Nature 220, 436 (1968). IX Voor het meten van de spontane magnetisatie en van de gemiddelde domeingrootte in de transmissierichting van een ferromagneet met mvoudige wijze lage tem- behulp van neutronen-depolarisatie, zijn bij gegeven reactorflux en thermische effecten te gelet op de beschikbare polariseertechnieken, koude neutronen (met van electronen. een golflengte van ongeveer 4 A) te prefereren boven thermische (1 A). de gravitatíestraling Het besturen van een land als Nederland kan slechts door een multidisciplinair team van deskundigen worden overzien en uitgevoerd. g ook de polarisatie Dit leidt voor de niet-gespecialiseerde buitenstaander (de overgrote meerderheid van de bevolking) tot een onduidelijkheid in de politiek 94 (1972). die maar zeer ten dele door vereenvoudiging van de partijverhoudingen kan worden verbeterd. geldigheid van de A.Th.A.M. de Waele 21 december 1972 :raling in twijfel eussischen Akademie 8). BLI SUPERCONDUCTING POINT CONTACTS WEAKLY CONNECTING TWO SUPERCONDUCTORS AND ELECTROSTATIC EFFECTS IN SUPERCONDUCTORS DUE TO TEMPERATURE GRADIENTS PROEFSCHRIFT TER VERKRIJGING VAN DE GRAAD VAN DOCTOR IN DE WISKUNDE EN NATUURWETENSCHAPPEN AAN DE RIJKSUNIVERSITEIT VAN LEIDEN, OP GEZAG VAN DE RECTOR MAGNIFICUS DR. A. E. COHEN, HOOGLERAAR IN DE FACULTEIT DER LETTEREN, VOLGENS BESLUIT VAN HET COLLEGE VAN DEKANEN TE VERDEDIGEN OP DONDERDAG 21 DECEMBER 1972, TE KLOKKE 14.15 UUR DOOR ALPHONS THEOPHILE AUGUSTA MARIA DE WAELE GEBOREN TE KOEWACHT (THANS GEMEENTE AXEL) IN 1944 1972 DRUKKERIJ J. H. PASMANS, 'S-GRAVENHAGE Promotor: Dr. R. de Bruyn Ouboter f .s; §6 §7 §9 §10 CONTENTS General Introduction PART I SUPERCONDUCTING POINT CONTACTS WEAKLY CONNECTING TWO SUPERCONDUCTORS Contents of Part I 11 §i Introduction 12 Two superconductors weakly connected by a single §2 superconducting point contact 24 The critical current through a double point contact §3 between two superconductors as a function of the applied magnetic field 38 §4 Two superconductors weakly connected by a double point contact in the resistive-superconductive region 50 §5 Description of the experimental set-up and the con- struction of double point contacts 69 : «ví' PART II Ml ELECTROSTATIC EFFECTS IN SUPERCONDUCTORS DUE TO TEMPERATURE GRADIENTS Contents of Part II 75 §6 Introduction 76 §7 Analysis of the measuring method; discussion of the effects contributing to the electrostatic signal 85 §8 Description of the apparatus. Noise sources and erroneous signals 92 §9 Experimental results 99 §10 Conclusions of Part II 103 References 104 Samenvatting 108 (§ Pir. (s GENERAL INTRODUCTION The work described in this thesis deals with the macroscopic quantum effects in superconducting point contacts weakly connecting two super- conductors and with the electrostatic effects in superconductors due to temperature gradients. When two superconductors are completely isolated from each other it is possible to apply a voltage difference between both superconductors, while there is no current flowing between them (V = any value, i = 0). On the other hand, when two superconductors are tightly pressed against each other a supercurrent can flow through the contact region while the voltage is zero (V = 0, i = any value below the (bulk) critical current). From these considerations one can understand that there should be ways of connecting two superconductors that lead r.o current-voltage dependen- ces that are in some way in between these two extreme (and trivial) cases. In order to find this intermediate region one must "weakly" con- nect the two superconductors. In 1962 and 1963 Josephson and Anderson predicted that weakly coupled superconductors should show a macroscopic quantum behaviour. There are many ways to realize a weak coupling. One can separate the two superconductors by a thin insulation layer (tunnel junction), a layer of a normal metal (S-N-S junction) or by a narrow constriction of super- conducting material (Dayem bridge) with a width of the order of one micro- meter. The types of weak links that we deal with in part I of this thesis (§1 - §5) are the so-called superconducting point contacts. They con- sist of one or more points of one superconducting block that touch another superconducting block. Although the detailed behaviour of the various types of weak links is different, they have many important features in common. One of them is that up to a certain critical value a current can flow through the weak link while the voltage across the link is zero, even in an oxide or an S-N-S junction. Another common feature is that weak links radiate electro-magnetic waves, obeying the relation 2eV = hv. These effects were predicted by Josephson in 1962. Part I of this thesis deals with the dc and ac current-voltage- magnetic field dependences of several different point contact arrange- ments. It is shown (§2) that in a device with a single supeiconducting point contact, ac super and normal currents, and ac and dc voltages are generated when a dc current is supplied to the contact, larger than the maximum supercurrent (V í 0).
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