THE DISCOVERY OF TUNNELLING SUPERCURRENTS Nobel Lecture, December 12, 1973 Cavendish Laborate ambridge, England The events leading to the discovery of tunnelling supercurrents took place while I was working as a research student at the Royal Society Mond Labo- ratory, Cambridge, under the supervision of Professor Brian Pippard. During my second year as a research student, in 1961-2, we were fortunate to have as a visitor to the laboratory Professor Phil Anderson, who has made numerous contributions to the subject of tunnelling supercurrents, including a number lf. His lecture Cambridge introduced the new concept of 'broken symmetry' in supercon- ductors, (1)which was already inherent in his 1958 pseudospin formulation of superconductivity theory, (2 which I shall now describe As discussed by Cooper in his Nobel lecture last year (3)according to the Bardeen-Cooper-Schrieffer theory there is a strong positive correlation in a uperconductor between the occupation of two electron states of equal and opposite momentum and spin. Anderson showed that in the idealized case where the correlation is perfect the system can be represented by a set of inter acting pseudospin, with one pseudospin for each pair of electron states The situation in which both states are unoccupied is represented by a pseude spin in the positive z direction, while occupation of both states is represented in the negative z direction; other pseudospin orientations orrespond to a superposition of the two possibilities The effective Hamiltonian for the system is given by H=-2∑(ek-)5-∑vk(skx5kx+ysty) (1) the first term being the kinetic energy and the second term the interaction energy. In this equation Skrnky and Skz are the three components of the k seudospin. E k is the single-particle kinetic energy, u the chemical potential and Vkk the matrix element for the scattering of a pair of electrons of equal and opposite momentum and spin. The k"pseudospin sees an effective field H=2(Ek-1)+2∑Vksk⊥ where z is a unit vector in the z direction and indicates the component of the pseudospin in the xy plane One possible configuration of pseudospin consistent with(2)is shown in Fig. 1(a). All the pseudospin lie in the positive or negative z direction, andTHE DISCOVERY OF TUNNELLING SUPERCURRENTS Nobel Lecture, December 12, 1973 by B RIAN D. J OSEPHSON Cavendish Laboratory, Cambridge, England The events leading to the discovery of tunnelling supercurrents took place while I was working as a research student at the Royal Society Mond Labo￾ratory, Cambridge, under the supervision of Professor Brian Pippard. During my second year as a research student, in 1961-2, we were fortunate to have as a visitor to the laboratory Professor Phil Anderson, who has made numerous contributions to the subject of tunnelling supercurrents, including a number of unpublished results derived independently of myself. His lecture course in Cambridge introduced the new concept of ‘broken symmetry’ in supercon￾ductors, (1) which was already inherent in his 1958 pseudospin formulation of superconductivity theory, (2) which I shall now describe. As discussed by Cooper in his Nobel lecture last year (3) according to the Bardeen-Cooper-Schrieffer theory there is a strong positive correlation in a superconductor between the occupation of two electron states of equal and opposite momentum and spin. Anderson showed that in the idealized case where the correlation is perfect the system can be represented by a set of inter￾acting ‘pseudospins’, with one pseudospin for each pair of electron states. The situation in which both states are unoccupied is represented by a pseudo￾spin in the positive z direction, while occupation of both states is represented by a pseudospin in the negative z direction; other pseudospin orientations correspond to a superposition of the two possibilities. The effective Hamiltonian for the system is given by the first term being the kinetic energy and the second term the interaction energy. In this equation skr,sli. and sliz are the three components of the kth pseudospinck is the single-particle kinetic energy, µ the chemical potential and Vlilz’ the matrix element for the scattering of a pair of electrons of equal and opposite momentum and spin. The kth pseudospin sees an effective field where i is a unit vector in the z direction and 1 indicates the component of the pseudospin in the xy plane. One possible configuration of pseudospins consistent with (2) is shown in Fig. 1 (a). All the pseudospins lie in the positive or negative z direction, and