Prof. Dr. Brian David Josephson > Research Profile
by Roberto Lalli
Brian David Josephson
Nobel Prize in Physics 1973 "for his theoretical predictions of the properties of a supercurrent through a tunnel barrier, in particular those phenomena which are generally known as the Josephson effects".
Brilliant Beginning in Theoretical Physics
Brian D. Josephson was born in Cardiff, the capital of Wales, on January 4, 1940, to Abraham Josephson and Mimi Weisbard. After having become interested in theoretical physics during his secondary education at Cardiff High School, in his undergraduate studies Josephson read the mathematical tripos at the eminent Trinity College, Cambridge University. After two years, however, he decided to switch to physics proper because he found the mathematical approach to physical problems too unrealistic. To his professors, Josephson appeared as an extremely brilliant, albeit shy, student. His ability to quickly master the novel developments in theoretical physics became evident when he wrote his first important paper in that field as an undergraduate.
In 1958, the German physicist Rudolf L. Mössbauer had observed a resonance of gamma rays in solid iridium. As opposed to x-rays, the emission and absorption of gamma rays had never been observed before that year. While x-rays are primarily emitted during electronic transitions, gamma rays are emitted in nuclear transitions, and previous attempts at observing nuclear resonance in gases had failed because the emission process causes the recoil of the emitting nucleus. As a consequence, the emitted gamma rays do not have sufficient energy to excite the target nuclei.
Not only had Mössbauer observed gamma ray resonances for the first time, but he had also put forward a mechanism that explained why gamma rays resonance occurred in solids, but not in gases. He attributed the effect to the fact that, under certain circumstances, the solid state prevents the nucleus from recoiling, thus preserving the entire energy for the emitted gamma rays. In Mössbauer’s view, the entire crystal to which the emitting nucleus was bound absorbed the recoil thereby reducing to a negligible portion the quantity of energy lost. The effect observed and explained by Mössbauer soon became a fundamental experimental tool for precise observations in physics and chemistry.
Published in 1960, Josephson’s first paper dealt with the theoretical understanding of the Mössbauer effect and especially with its application to the observation of the gravitational redshift—a well-known empirical implication of Einstein’s theory of general relativity. Josephson demonstrated that previous calculations had overlooked that extremely tiny temperature differences between the emitting and receiving nuclei could dramatically affect the observations of gravitational redshift done by means of the Mössbauer effect.
The Discovery of the Josephson Effect
After having earned his bachelor’s degree in 1960, Josephson decided to pursue graduate studies in experimental physics at the Royal Society’s Mond Laboratory of Cambridge University under the supervision of Brian Pippard—a British physicist who was making his name as a world expert in solid-state physics. Among other contributions, Pippard had dedicated many efforts to the understanding of the phenomenon of superconductivity. After World War II, Pippard performed various experiments on the properties of superconductors, especially concerning their response to microwave radiation. One of his experimental findings was that the penetration depth increased as the impurity increased. In order to theoretically explain this empirical fact, Pippard put forward a nonlocal reformulation of the London phenomenological theory of superconductivity. Pippard’s experimental and theoretical work was relevant to the theoretical advances that would eventually lead to the Bardeen-Cooper-Schrieffer theory of superconductivity (better known as BCS theory) in 1957. The BCS theory was the first microscopic theory that successfully derived the empirical phenomena related to superconductivity starting from the first principles of quantum mechanics. Experimental evidence gave strong support to the theory, but some theorists raised some doubts on the theoretical consistency of the theory. The most important of these criticisms focused on the apparent lack of gauge invariance of the BCS theory.
Pippard participated in the debate and closely followed its evolution. When Josephson began working with Pippard, the BCS theory was gaining momentum because of further experimental confirmation and a series of theoretical developments that had clarified the status of the BCS theory with respect to the theoretical problems raised by its critics. Among others, the American theoretical physicist Philip W. Anderson had been very involved in the clarification of the BCS theory, making important contributions to the resolution of the gauge invariance problem. Because of this and other important contributions to the theory of solids, Pippard invited him to join Cambridge University for a sabbatical year in 1961-62.
Under the influence of Pippard and, later, of Anderson’s lectures, the young Josephson became deeply interested in the phenomenon of superconductivity and in the BCS theory. He focused on the physical properties of a system made by two superconductors separated by a thin insulating layer—now called Josephson junction. The application of the BCS theory to this kind of systems led Josephson to discover unforeseen properties in 1962—an achievement that would gain him the Nobel Prize eleven years later.
Josephson got interested in the phenomenon of quantum tunnelling in solids after he became aware of recent observations made by I. Giaever that currents were able to flow from two metals (where either one or both of them were in the superconducting state) separated by a thin insulating film if the thickness of this film was sufficiently small.
Since 1926—when Schrödinger employed de Broglie’s work on the wave properties of particles to develop his wave equation to describe the change in time of a quantum system—quantum mechanics predicted that material particles could penetrate a thin potential barrier—a behaviour absolutely forbidden in classical physics. Empirical evidence led to a rapid acceptance of the novel quantum mechanics, and quantum tunnelling came to be considered as one of the physical effects that most strikingly differentiated quantum mechanics from Newtonian mechanics. While early confirmation of this effect emerged in the field of nuclear physics—when Gamow explained the emission of alpha rays as a quantum tunnelling effect that allowed the alpha particles to pass through the nuclear potential barrier—similar confirmation in the conduction of electrons in solids was much more difficult to achieve.
This state of affairs changed dramatically only in the last years of the 1950s. In 1957, the Japanese industrial physicist Leo Esaki provided convincing experimental evidence for electron tunnelling in semiconductors. After Esaki’s discovery was made public, the field of electron tunnelling in solids received much attention, often connected with its possible industrial applications. Two years later, the Norwegian physicist Ivar Giaever made a discovery that was even more influential for the development of Josephson’s own research project. Since the early 1950s, John Bardeen had been advocating that an energy gap appears in the passage from the normal to the superconducting state of metals. One of the main predictions of the successful BCS theory was the existence of such an energy gap. Giaever believed that the energy gap would have testable consequences on the tunnelling of electrons between metals separated by an insulating layer when one or both the metals where cooled down below their critical temperature. While in the tunnelling of electrons between two metals separated by an insulating film the current is proportional to the applied voltage, in a metal-insulator-superconductor junction the energy gap hypothesis implied that the current-voltage characteristic would be drastically altered. After having performed a series of experiments on quantum tunnelling in metals, Giaever decided to test the effect on the relationship between current and voltage implied by the BCS theory. With the support of many colleagues at the General Electric Laboratory, Giaever was able to successfully carry out his experiments employing lead and aluminium. The result was that as soon as one of the two metals (the lead) changed from the normal to the superconducting state, the current-voltage characteristic markedly changed in just the way expected by Giaever. As a second step, he also performed an experiment on two superconductors separated by a thin oxide layer. Even in this case, the result was as expected. Once the second metal also reached the superconducting state the resistance became negative.
Giaever’s results rapidly became one of the most interesting experimental novelties in the field of superconductivity. Besides being an accurate empirical confirmation of the BCS theory, Giaever’s discovery left many theoretical questions unexplained. These experiments, along with Anderson’s unpublished work on superconductive tunnelling and some particular features of the BCS theory, contributed to trigger Josephson’s intellectual curiosity resulting in the discovery of the Josephson effect. According to his recollections, Josephson was intrigued by Anderson’s pseudospinorial reformulation of the BCS theory, which made the spontaneous symmetry breaking of the theory manifest. One of the features of the spontaneous breakdown of symmetry in the BCS theory is that the wave function of the ground state of Cooper pairs has a definite phase in addition to an amplitude. Josephson got interested in the problem of whether this phase had observable consequences and, then, to find a way to empirically test the mechanism of spontaneous symmetry breaking in the superconducting state. The only way, Josephson’s reasoning went, to observe physical properties related to the phase in the BCS wave function was to look for phenomena related to the phase difference between two superconductors.
This train of thoughts led Josephson to focus on the recent experimental results obtained by Giaever. Josephson’s calculation showed that, besides the current observed by Giaever, one had to expect a weaker superconducting current due to tunnelling of Cooper pairs. Since the formation of Cooper pairs was the essential mechanism underlying the phenomenon of superconductivity, Josephson’s theory implied that supercurrents could flow through a barrier. Josephson’s calculations predicted two main effects. The first implication was that without applied potential one would observe the tunnelling of direct supercurrent, whose intensity was proportional to the phase difference between the Cooper pair functions in the two superconductors. The second one was that high frequency alternating supercurrents could flow through the barrier if a certain voltage was applied. The frequency of the oscillating supercurrents was independent of the properties of the superconductors and depended on universal constants through the formula 2eV/h (where e is the charge of the electron, h is the Planck constant, and V is the bias potential).
Josephson put forward his theory of superconducting tunnelling at the age of 22, when he was still a first-year graduate student. One of the problems of his theoretical calculations was that the effects predicted—the Josephson supercurrents—were so large that they should have been already observed in previous experiments performed by Giaever and others. Anderson, however, encouraged Josephson to publish his study, while Pippard suggested Josephson to perform the experiment on the tunnelling of supercurrents himself. Josephson followed both suggestions. The experiment he performed did not produce any positive results and ended up as a minor chapter of Josephson’s thesis. Josephson’s paper, however, was published in the newly established journal Physical Letters with the title “Possible New Effects in Superconductive Tunnelling” in 1962. Although very short, the paper contained the building blocks as well as the major predictions of Josephson’s theory of tunnelling of supercurrents in a superconductor-insulator-superconductor-system —an effect now universally known as Josephson effect.
The Rapid Acceptance of the Josephson Effect
Anderson reacted very positively to Josephson’s theoretical findings, but the majority of leaders of the solid-state community did not share Anderson’s enthusiasm. Some eminent theoretical physicists found very hard to understand Josephson’s theoretical formalism and its relationship with the hypothesised physical phenomena. Pippard himself believed that the simultaneous tunnelling of two electrons was virtually impossible on the grounds that even the tunnelling of single electrons was a very rare event. The eminent Nobel Laureate John Bardeen—who had headed the small theoretical team that had successfully developed the BCS theory—explicitly dismissed Josephson’s theory. In September 1962, Bardeen publicly challenged Josephson onthe reality of the effect at the Eighth International Conference on Low Temperature Physics in London. While Josephson argued that the mathematics of the BCS theory predicted the effect, Bardeen’s physical intuition led him to believe that electron pairing could not extend across the insulating barrier, however thin the insulating layer might be. The only way to solve the issue was by means of experimental tests.
As a matter of fact, a phenomenon attributable to the DC Josephson tunnelling had already been observed before Josephson elaborated his theory, in experiments performed by Giaever and, independently, by J. Nicol, S. Shapiro, and P. Smith. The effect, however, had been attributed to small breaches in the insulating layer due to the extreme thinness of the employed films. Anderson was soon enthusiastic about the work done by Josephson and began collaborating with the British experimental physicist John Rowell to test the DC Josephson effect at the AT&T Bell Telephone Laboratory.
In the meantime, Anderson was also building on Josephson’s work to make elaborate theoretical predictions, which had already been found by Josephson himself for his dissertation. This state of affairs resulted in a certain delay and confusion in the publication of the theoretical results. Josephson collected his own theoretical elaborations for an application to a research fellowship at Trinity College, but did not publish this work. This fellowship thesis contained the full account of the theory underlying the Josephson effect, as well as all its physical implications. Anderson received one of the few copies of Josephson’s work, which made him aware that Josephson had already published all the theoretical work Anderson had independently done. For this reason, Anderson decided not to publish his own research for he did not want to receive excessive credit for results that had already been obtained by the younger Josephson. Eventually, the full account of the Josephson effect was not easily available and several of the earlier findings even had to be re-discovered at a later period.
Anderson, however, successfully carried out with Rowell the experimental part of his research project on the DC Josephson effect, and in 1963 they published the first paper to explicitly claim for the empirical observation of the effect. By showing the dependence of the effect on the varying magnetic field, Anderson and Rowell proved that the effect could not depend on metallic shorts. A few months after Anderson and Rowell’s confirmation, the second prediction of Josephson’s theory—namely, the insurgence of AC supercurrent tunnelling—was also confirmed, although in an indirect way. Shapiro published his observations of constant current-voltage steps induced by the frequencies of microwave radiation.
Once these experiments provided convincing evidence for the reality of the Josephson effect, it was rapidly accepted by the majority of physicists working in the field of condensed matter. Remarkably, the empirical confirmation of the Josephson effect also became a confirmation of the validity of the BCS theory as well as of its physical implications. The Josephson effect became relevant as a tool in a variety of applications in physics and engineering such as, e.g., the SQUIDs (the Superconducting Quantum Interference Devices, which are extremely sensitive magnetometers) and the precise measurement of e/h ratio, as the frequency of AC Josephson supercurrents depends on this ratio. The great importance of Josephson’s breakthrough lies in the fact that a microscopic quantity (namely, the phase-dependent energy) had an observable influence on macroscopic variables.
In 1973, the year after Bardeen, L. Cooper and J. Schrieffer were jointly awarded the Nobel Prize in Physics for the discovery of the BCS theory, Josephson received one half of the Nobel Prize in Physics “for his theoretical predictions of the properties of a supercurrent through a tunnel barrier, in particular those phenomena which are generally known as the Josephson effects.” Leo Esaki and Ivar Giaever shared the other half of the 1973 Nobel Prize in Physics for their related research concerning the tunnelling phenomena in semiconductors and superconductors.
Theoretical physics and the mind-body problem
The Josephson effect had already been accepted as one of the most striking features of superconductivity and one of the most useful consequences of the BCS theory, when Josephson earned his PhD in 1964 with a dissertation entitled “Non-linear conduction in superconductors.” After his PhD, Josephson spent one year as visiting research professor at the University of Illinois. Apart from this experience in the USA, Josephson remained at Cambridge University all through his professional career till his retirement in 2007. In the 1960s, Josephson continued to do research on solid-state physics as a member of the Theory of Condensed matter group at the Cavendish Laboratory contributing to the theory of superconductivity and with a series of investigations on critical phase transitions.
After he received the Nobel Prize, Josephson became one of the few authoritative physicists to publicly legitimise paranormal phenomena as something worth of scientific investigation. In the late 1960s, Josephson got interested in parapsychology with the explicit aim of looking at the possible connections between the unintuitive physical implications of quantum mechanics and the possible physical interactions between mind and material world implied by allegedly observed paranormal phenomena. This unusual approach to theoretical physics probably developed in the early 1970s when he started practicing Transcendental Meditation—a meditation technique that was becoming very popular in that period. The winning of the Nobel Prize in 1973 suddenly contributed to an improvement of his working condition, leading to his promotion to professor of physics at Cambridge. It also provided Josephson more freedom to pursue his own interests. In the following years, Josephson tried to extend the range of action of theoretical physics in other fields usually unexplored in this kind of activity. The main idea developed from Bell’s theorem and its possible implications on consciousness as well as from one of the most striking features of quantum mechanics—according to which the observer influences the observations. For Josephson, it was meaningful to freely extrapolate from these properties of quantum mechanics in the attempt to understand those relationships between consciousness and the material world that go under the name of paranormal occurrences.
Although harshly criticized for his research in these fields—which was largely considered as wild speculation and an undue extension of the scientific range of action—Josephson remained firm in his conviction that the scientific community usually act on the basis of consensus and that paranormal phenomena deserved much more attention than modern scientists were disposed to give. In the 1970s, other physicists were developing a similar interest in the possible implications of quantum mechanics (especially Bell’s theorem and quantum entanglement) for some paranormal activities such as psychokinesis and clairvoyance. A group of physicists, some of them associated with the University of California at Berkeley, began investigating paranormal claims on physical grounds and actively participated in the research on parapsychology at the Stanford Research Institute. The Fundamental Fysiks Group—as they began to call their free association—organized, or was part of, several activities aimed at promoting a quantum mechanical approach to parapsychology. Josephson participated in some of these activities and also publicly defended this kind of approach against the views of the majority of his fellow physicists.
The contributions of Josephson to these kinds of research have been numerous and very controversial. He has tried to apply complex theoretical formalism to issues such as psycholinguistics, music, complex systems, and artificial intelligence. These interests led him to establish a research project entitled Mind-Matter Unification Project at Cavendish Laboratory in 1996. Since the 1970s, his work has been considered at the fringe of scientific research and his opposition to widely held views has led to strong public controversies with his colleagues and authoritative journals such as Nature, whose publication policies he strongly criticised. Josephson also defended scientific hypotheses and experimental findings, such as water memory and cold fusion, which were commonly considered as pseudo-scientific or, even worse, scientific hoaxes.
In view of his opinion on these kinds of issues, Josephson occupies an almost unique niche at the boundary between the authoritative status provided by his Nobel Prize—and his undeniable ability in theoretical physics—and a fringe status related to his more recent, although long-lasting, convictions. Up to this day, Josephson continues to enjoy his borderline position to promote his views and attack the scientific criteria often utilized to dismiss his own work as well as that of other scientists who do not have the support of their communities.
Bibliography
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Brian David Josephson (2009) HowStuffWorks.com. Retrieved on January 4, 2015.
http://science.howstuffworks.com/dictionary/famous-scientists/physicists/brian-david-josephson-info.htm
Cooper, L. N., & Feldman, D. (eds.) (2011) BCS: 50 years. World Scientific, Singapore.
Hoddeson, L., Braun, E., Teichmann, J., & Weart, S. (eds.) (1991) Out of the Crystal Maze: Chapters from the History of Solid-State Physics. Oxford University Press, New York.
Interview of Philip Anderson with Alexei Kojevnikov. On Novemer 23, 1990. Niels Bohr Library & Archives, American Institute of Physics, College Park, MD USA. Retrieved on December 14 2014
http://www.aip.org/history/ohilist/23362_3.html
Josephson, B. D. (1973) Nobel Lecture: The Discovery of Tunnelling Supercurrents. In Stig Lundqvist (eds.) (1992) Nobel Lectures, Physics 1971-1980. World Scientific Publishing Co., Singapore, pp. 157-164.
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Press Release: The 1973 Nobel Prize in Physics. Nobelprize.org. Nobel Media AB 2014. Retrieved 10 January 2015. http://www.nobelprize.org/nobel_prizes/physics/laureates/1973/press.html