For those of us who had the pleasure of knowing him in his mature years, Nicolás Cabrera comes as close as humanly possible to the ideal figure of a renowned scientist and a perfect gentleman, someone who has a keen insight in the ways of nature and at the same time is fully at ease with his fellow humans, always benevolent and encouraging, yet also reserved and detached in his judgment. Science and academics were in his family line, as he was the son of Blas Cabrera, the leading physicist in Spain between the two world wars. He was given by birth the opportunity to study and work with famous people in France and England, and happily his natural talent was up to the challenge and thrived on it. But he also knew sorrow in his life as an exile from a country torn by civil strife. In his years in North America, there was always an undertone of sadness in his eyes and a longing to return to a free and democratic Spain.
Jack Mitchell recalls that the Cabreras were living in an apartment in Paris when he recruited Nicolás to come to Bristol and work with Neville Mott as a post-doc. In Bristol he produced not only the fundamental theory of crystal growth, but also, with Mott, an important paper on the theory of the oxidation of metals [1]. It was perhaps this work that most impressed Allan Gwathmey of the Chemistry Department at the University of Virginia, and led him to arrange with Jesse Beams, then Chairman of Physics, to offer Cabrera a position, which he accepted in 1952. His scientific and leadership impact at Virginia extended also to Materials Science and other areas of Engineering, as he actively pursued interdisciplinary contacts, and his work transcended narrow boundaries.
My personal recollections of Cabrera date from a splendid spring day in 1962, when I came to give a seminar on dislocation dynamics at the University of Virginia. Those were the happy days in which young physicists did not have to apply for jobs, and I was barely aware of the fact that this was, in effect, an interview. Cabrera, who had just become Chairman, took a genuine interest in what I was doing, asked penetrating questions, and at the same time made me feel completely at ease, no small feat considering that I knew he was an author of the Burton-Cabrera-Frank theory of crystal growth [2], which was already enshrined in textbooks then (and appears even more fundamental today, more than fifty years later). Cabrera was a very effective recruiter at all levels, making effortless use of his natural charm and cultivated European style in personal contacts, and keeping a high awareness of possible candidates through his high-level contacts in the scientific world. Four years later, when I arrived in Charlottesville as the newest faculty member, Cabrera himself came to meet us at the station, which impressed my wife no end.
With Jack Mitchell, Doris Wilsdorf and her husband Heinz (in Materials Science) Virginia was then a leading center of research on dislocations and mechanical properties. Cabrera, however, was always looking for fresh fields. When he called me to his office to tell me of problems he had in mind, I was surprised (but should not have been) that it had nothing to do with crystal growth or dislocations. Instead, he told me of experiments under way in Aerospace Engineering on atom-surface interactions. He thought that atom scattering could be used to detect surface phonons, analogously to neutron scattering in the bulk. The kinematics was right but some approximate cross sections had to be computed to prove that the method was feasible. It sounded complicated enough that we needed a graduate student to help, and as it happened Dick Manson had just asked me for a thesis project. After we read up on scattering theory and surface elastic waves, everything turned out pretty much as Cabrera had anticipated for a simple elastic hard wall [3]. Actual surfaces are much more complicated, as we learned from Frank Goodman, who was working with the Aerospace people. The four of us hammered out a long paper [4], which required some effort to develop a common language, coming as we did from different specialties. Cabrera kept us together, focussing on the physics, and we deferred to him, naturally. This is something I have seen happen repeatedly in collaborations with him. He was a good listener and a natural leader; he did not dominate a discussion but came to the essential point, noting quickly where there was a real disagreement and where it was just a matter of semantics.
In 1967 Cabrera went on leave for a year in Caracas, and then accepted a leadership post at the resurgent Autonomous University of Madrid when Franco was still in power. There were several reasons for these developments. The Physics Department at Virginia had grown and prospered under Cabrera’s leadership, not only in Solid State, but also in Nuclear Physics. Unfortunately, some of the senior people had strong and apparently incompatible personalities, although they all had good relations with Cabrera. His patience and diplomatic skills were taxed, especially after some petty problems developed over the management of the nuclear facilities. Scheming and pettiness were so alien to his nature that he was saddened by them, and also felt that he had better ways to spend his time and energy. Although the Cabrera children had grown up as Americans and Blas, then enrolled at Virginia, was clearly on his way to his own physics career in the U.S., nostalgia for Spain was always near the surface, especially for Nicolás’s lively wife, Carmen. There were evenings at the Cabreras with singing and guitars, and as the party took wing more and more of the songs were Spanish. But fundamentally it was Nicolás who felt an obligation to return to Spain and rebuild science there.
That it took courage and dedication to do so was apparent to me at the Varenna Summer School on `Dynamic Aspects of Surface Physics’ in 1974, organized and directed by Frank Goodman. Although several aspects of surface physics were covered at this school, it was a seminal event in the field of atom-surface interactions, with Boato and Cantini reporting their high-quality diffraction data, Giorgio Benedek lecturing on surface phonons, and J.P. Toennies as one of the `students’ absorbing it all and preparing to make the study of surface phonons by He scattering a reality in his laboratory. Cabrera was expected to be one of the main lecturers, but he was able to attend only part of the time, as the situation in Spain had taken a turn for the worse. Incidentally, he was accompanied by Javier Solana, who was then his assistant in Madrid, before embarking on his still-rising political career. (He had come to Virginia to complete his graduate studies shortly before Cabrera left).
Things were dramatically different in 1980, when I was Cabrera’s guest at the Autonomous University of Madrid, in the Institute that now bears his name. He was now Don Nicolás, an almost legendary figure to the young generation of physicists in his own country. Those were heady days for Spain and its reborn democracy. Cabrera’s dreams and hopes had come true, and yet he was still striving for improvement, trying to set up his institution in a new, less bureaucratic way. In the midst of all the political excitement and the administrative struggles, he still found time to take out a yellow notepad, legal size, and work out equations and ideas.
Nicolás Cabrera was not driven by ambition or the hunger for recognition; after recognition and power came to him, he was as gentle and considerate as before. He knew adversity and acknowledged that the world is far from perfect, but remained an incurable optimist and was simply convinced that if one does the right thing it will all work out. And in the end it did.
V. Celli
Department of Physics,
University of Virginia
References
[1] Cabrera N and Mott N F 1999 Rep. Prog. Phys. 12 163
[2]Burton W C, Cabrera N and Frank F C 1951 Trans. Roy. Soc. (London) A243 299
[3]Cabrera N, Celli V and Manson R 1969 Phys. Rev. Letters 22 346
[4]Cabrera N, Celli V, Goodman F O and Manson R 1970 Surf. Sci. 19 67