ELECTRON TUNNELING AND SUPERCONDUCTIVITY Nobel Lect ure, Dece mber 12, 1973 b y I V A R G I Æ V E R General Electric Research an d Develo p ment Center, Schenecta dy, N. Y., US A. I n my laboratory notebook date d May 2, 1960 is t he e ntry: “Fri day, A pril 22, I perfor me d the follo wing ex peri ment ai me d at meas uring the forbi d den ga p i n a s u perco n d uctor.” T his was obvio usly a n extraor di nary eve nt not o nly be- ca use I rarely write i n my notebook, b ut beca use t he s uccess of t hat ex peri- me nt is t he reaso n I have t he great ho nor a n d pleas ure of a d dressi ng yo u t o d a y. I s h all tr y i n t his l e ct ur e, as b est I c a n, t o r e c oll e ct s o m e of t h e e v e nts a n d t h o u g hts t h at l e d t o t his n ot e b o o k e ntr y, t h o u g h it is diffi c ult t o d es cri b e w hat no w a p pears to me as fort uito us. I ho pe t hat t his perso nal a n d s ubjec- ti v e r e c oll e cti o n will b e m or e i nt er esti n g t o y o u t h a n a stri ctl y t e c h ni c al l e c- t ure, partic ularly si nce t here are no w so ma ny goo d revie w articles deali ng with s u percon d uctive t unneling. 1, 2 A rece nt hea dli ne i n a n Oslo pa per rea d a p proxi mately as follo ws: “ Mas- ter i n billiar ds a n d bri d ge, al most fl u n ke d p h ysics - gets Nobel Prize.” T he p a p er r ef ers t o m y st u d e nt d a ys i n Tr o n d h ei m. I h a v e t o a d mit t h at t h e r e p ort- i n g is reas o na bl y acc urate, t heref ore I s hall n ot atte m pt a “c o ver u p”, b ut co nfess t hat I al most fl u n ke d i n mat he matics as well. I n t hose da ys I was not ver y i ntereste d i n mec ha nical e n gi neeri n g a n d sc hool i n ge neral, b ut I di d ma nage to gra d uate wit h a n average degree i n 1952. Mai nly beca use of t he ho usi ng s hortage w hic h existe d i n Nor way, my wife a n d I fi nally deci de d to e migrate to Cana da where I soon foun d e mploy ment with Cana dian General Electric. A three year Co m pany co urse in engineering an d a p plie d mathe mat- ics k no w n as t he A, B a n d C co urse was offere d to me. I realize d t his ti me t hat sc hool was for real, a n d si nce it probably wo ul d be my last c ha nce, I really st u die d har d for a fe w years. W he n I was 28 years ol d I fo u n d myself i n Sc he necta dy, Ne w York w here I disco vere d t hat it was possible for so me peo ple to make a goo d li vi ng as physicists. I ha d worke d on vario us Co m pany assign ments in a p plie d mathe- matics, an d ha d develo pe d the feeling that the mathe matics was m uch more a dva nce d t ha n t he act ual k no wle dge of t he p hysical syste ms t hat we a p plie d it to. T h us, I t ho ug ht per ha ps I s ho ul d lear n so me p hysics a n d, e ve n t ho ug h I was still a n e n gi neer, I was gi ve n t he o p p ort u nit y t o tr y it at t he Ge neral Electric Researc h Laboratory. T he assig n me nt I was gi ve n was to work wit h t hi n fil ms a n d to me fil ms meant photography. Ho we ver I was fort u nate to be associate d wit h Jo h n Fis her w ho ob vio usly ha d ot her t hi ngs i n mi n d. Fis her ha d starte d o ut as a mec ha nical e n gi neer as well, b ut ha d latel y t ur ne d his atte n- 1 3 8 Fi g. 1. A. If a ma n t hro ws a ball agai nst a wall t he ball bo u nces bac k. T he la ws of p hysics allo w t he b all to pe netr ate or t u n nel t hro ug h t he w all b ut t he c h a nce is i nfi nitesi m ally s mall beca use t he ball is a macroscopic object. B. T wo metals separated by a vac u u m will a p proxi mate t he above sit uatio n. T he electro ns i n t he metals are t he “balls”, t he vac u u m represe nts t he wall. C. A pictorial e nergy diagra m of t he t wo metals. T he electro ns do not have e no ug h e nergy to escape i nto t he vac u u m. T he t wo metals ca n, ho wever, exc ha nge electro ns by t u n neli ng. If t he metals are s pace d close toget her t he probability for t u n neli ng is large beca use t he electro n is a microscopic particle. tion to war ds theoretical physics. He ha d t he notio n t hat usef ul electro nic d e vi c es c o ul d b e m a d e usi n g t hi n fil m t e c h n ol o g y a n d b ef or e l o n g I w as w or k- i n g wit h m et al fil ms s e p ar at e d b y t hi n i ns ul ati n g l a y ers tr yi n g t o d o t u n n eli n g ex peri ments. I have no do ubt that Fisher kne w abo ut Leo Esaki’s t unneling ex peri me nts at t hat ti me, b ut I certai nl y di d not. T he co nce pt t hat a particle ca n go t hro ug h a barrier see me d sort of stra nge to me, j ust str uggli ng wit h q ua nt u m mec ha nics at Re nsselaer Polytec h nic I nstit ute i n Troy, w here I took f or mal c o urses i n P h ysics. F or a n e n gi neer it s o u n ds rat her stra n ge t hat if y o u I. Gi a e v er 1 3 9 Fi g. 2. A sc he matic dra wi ng of a vac u u m syste m for depositi ng metal fil ms. For exa mple, if al u mi n u m is heate d resistively i n a ta ntal u m boat, t he al u mi n u m first melts, t he n boils a nd evaporates. T he al u mi n u m vapor will solidify o n a ny cold s ubstrate placed i n t he vapor strea m. T he most co m mo n s ubstrates are ordi nary microscope glass slides. Pat- ter ns ca n be for med o n t he slides by s uitably s hieldi ng t he m wit h a metal mask. t hr o w a t e n nis b all a g ai nst a w all e n o u g h ti m es it will e v e nt u all y g o t hr o u g h wit ho ut da ma gi n g eit her t he wall or itself.