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LEOPOLDO MAXIMO FALICOV Tune 24, 1933-January 24, 1995 BY MANUEL CARDONA, MARVIN L. COHEN, AND STEVEN G. LOUIE LEOPOLDO ("LEO") MAXIMO Falicov died onJanuary 24, 1995, after a short illness involving cancer of the esophagus. He was a professor of physics at the University of California, Berkeley, en cl a specialist in the theory of conclensecl matter physics. He was elected to membership in the National Academy of Sciences in 1983. He was also a member of the Academia Nacional cle Ciencias Exactas, Fisicas y Naturales of Argentina, and the Royal Danish Academy of Sciences en cl Letters. He was a fellow of the American Physical Society, Britain's Institute of Physics, en cl the Third WorIcl Academy of Sciences. He receiver! numerous fellowships, inclucling the Sloan, Fulbright, and Guggenheim fellowships, and an honorary cloctor of science degree from the University of Cambridge. Falicov's early (postcloctoral) work, performed at the University of Cambridge (EnglancI, 1958-60) establishecl en cl eTuciciatec! the complex nature of the electronic bane! structures of metals (such as magnesium, aluminum, zinc, cadmium en cl the cletails of their Fermi surfaces (1962,1~. At the University of Chicago (1960-69) he proposer! the existence of magnetic breakdown in metals that possess small energy band gaps and coauthored an important paper on superconductive tunneling ~ ~ 962,2) . At Berkeley ~ ~ 969-95) 19

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20 B I O G RA P H I C A L EMOIRS he was also responsible for a number of "firsts" in theoretical condense cl matter physics , in clucling the so-calle cl Falicov- Kimball theory of semiconcluctor-metal transitions (1970), the theory of resonant photoemission (1977), resonant Ram an scattering (1973), en cl many others. A book on group theory en cl its applications to solicI-state physics (1966), basecl on a course he taught at the University of Chicago en c! now out of print, has been a stanciarcl textbook to a couple of gen- erations of conclensecI-matter physicists. Falicov's theoreti- cal work was complemented! through strong interactions with experimentalists. Because of his talent for spatial visualiza- tion, Falicov's theories were often geometrical en cl very clearly clefinecI. The intense experimental research on Fermi sur- faces of metals en cl semimetals in the 1960s en cl 1970s re- sultecl in ciata that couIcl be viewocl as parts of puzzles. Falicov's work on Fermi surface geometries allowed! consistent inter- pretation of the ciata en cl brought the pieces of the puzzles together. Some of his drawings of Fermi surfaces were con- siclerec! to be works of art, such as the "FaTicov monster" moclel for magnesium en cl his "poisoned turnips" moclel for arsenic. These pictures have been reproclucecl in stan- ciarc! textbooks en c! on covers of conference proceedings. His great command of geometry en cl symmetries was reflected in the excellent text he wrote on group theory. Leo FaTicov was born in Buenos Aires, the fecleral capital of Argentina, on June 24, 1933. His parents were both of Eastern European Jewish origin. His father, Issues Felix FaTicov, was born in Argentina, whereas his mother, Dora Samoilovich, immigrated to Argentina with her parents at an early age. It seems that her father left southern Russia to avoic! being ciraftec! into the Russo-lapanese War. Those of us who knew Leo for many years were very aware of his Argentinean roots, which reflected themselves not only in

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LEOPOLDO MAXIMO FALICOV 21 his speech (both in Spanish en c! in English) but also in his attitudes en cl his gentle, milcI-mannerecl temperament. Leo's parents both stucliecl clental medicine at the Uni- versity of Buenos Aires, where they probably met. While this may sound surprising given their recent immigrant Jewish background, one must keep in mincl that Argentina was at the turn of the twentieth century one of the woricl's strongest economies en cl an immigrant's paradise. Compulsory en cl free lay public education hacl been establishecl in the micI- ~ SOOs by D. F. Sarmiento, the first civilian president of Argentina. The quest for higher education en cl learning found fertile ground in Argentina at the turn of the twentieth century. In spite of the available opportunities the economic realities of early immigrants compellecl Leo's parents to stucly dentistry, a professional course that was not only one of the shortest in those clays but also proviclec! financial inclepenclence at an early age. The Falicov-Samoilovich couple also hacl a son, Raul, four years younger than Leo. Raul stucliec! medicine in Argentina en c! also immigrates! to the Unitecl States (Argentina is often mentioned as one of the few countries in the worIcl with a serious brain cirain prob- lem). RauT liver! in San Diego until he succumbec! to can- cer in 1989. Leo's parents also hacl a daughter, Estela, who was 10 years younger than Leo. Estela, a sociologist, now lives in Buenos Aires. Like most Argentineans, Leo attenclecl public grammar school (in Buenos Aires) en cl then a highly prestigious public high school, the Colegio Nacional cle Buenos Aires. He gracluatecl in all cases with the highest gracles en cl honors. We have attempted, without success, to final out whether any specific person may have exercised a significant influ- ence on his analytical and mathematical abilities en cl interests. His father seems to have had a general interest in mathe- matics and, even more so, in games that requires! consiclerable

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22 B I O G RA P H I C A L EMOIRS intellectual effort, such as bridge. Leo inheritec! his father's interests en cl clevelopecl remarkable skills in such pastimes (he won a number of bridge championships). After graduat- ing from the Colegio Nacional cle Buenos Aires, Leo enterer! the state-ownecl School of Engineering en cl Natural Sciences at the University of Buenos Aires en cl remained in his parents' home cluring the ensuing studies. As with many other aclo- lescents, this must have been a period of consiclerable soul searching for Leo, in particular concerning his professional interests en c! future. He hesitater! between an engineering en cl a chemistry curriculum. He remained in Buenos Aires until 1955, when he movecl to Bariloche, managing to obtain a Jicenciaclo degree (something between a bachelor en c! a master, common in Spanish-speaking countries) in chemistry from Buenos Aires in 1957, after only two years of residence in Bariloche en c! in spite of the heavy workload! there. We have Earned that while a student at the University of Buenos Aires, Leo became a very close friend of two highly gifted young men, Enrique Bonacalza (who was murclerecl in 1997 near Bariloche) en cl Ecigarclo Slemenson. Early in 1955 they must have heard that a new graduate school of physics was about to open in San Carios cle Bariloche, a beautiful spot at the foot of the Patagonian Ancles, locatecl in splenclicl isolation 1,800 kilometers away from Buenos Aires, straight line, on the shore of Lake Nahue! Huapi. The new school was to be run by the Argentinean Atomic Energy Commission en cl not only wouIcl tuition be free but the students were all to receive a stipend to cover their living expenses. Corresponclingly, admission require- ments wouIcl be very strict (a policy, unusual in Latin America, that has been kept to the present clay). Leo en c! his frienc! Bonacalza appliecl for admission to the new school en cl hacl no difficulty passing the entrance examination. They both moved to Bariloche in the spring (our fall) of 1955 and

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LEOPOLDO MAXIMO FALICOV 23 gracluatec! with the Jicenciaclo degree in physics in 195S, Leo with the highest honors en cl as the valeclictorian of the first graduating class. Nearly simultaneously Leo wrote a cloctoral dissertation on the Lennuier effect (1960), an in- triguing phenomenon observed in Paris in 1947 by the cloc- toral student whose name it bears. The effect, as explainecl by Leo, involves quantum-mechanical frequency shifts in the resonance fluorescence of atomic vapors (e.g., mercury) at low pressure. To gain perspective about Leo en c! his career we must now cleIve into the series of bizarre events that lecl to the creation of what is now callecI, after its first director, the Instituto cle F~sica Balseiro, in a rather isolates! but extremely beautiful spot of the Argentinean Patagonia. WorIcl War II left Argentina, a country rich in foodstuffs en cl raw materials, in very goof! financial shape. Its liberal immigration policies hacl attracted a consiclerable number of European profes- sionals and intellectuals, among others, fugitives from Franco's dictatorship in Spain en c! from the anti-Semitism of other European dictators. They were joined at the end of the war by a few more escaping not only from the justice of the Allies but also from postwar devastation en c! penury. They gave a welcome boost to the bucicling Argentinean academic establishment. The physicists among them, how- ever, soon felt the frustration of their isolation, compounclec! by the ubiquitous secrecy that accompanied the atomic re- search performed by the nuclear powers. Some of the Argentinean physicists were able to approach President Peron, a populist military dictator, concerning the necessity for Argentina to clevelop its own nuclear program. In 1948 a young Austrian-German chemist (born in the Czech SudetenIand) by the name of Ronald Richter managed to gain access to Peron and to offer him a scheme to achieve, with rather simple means, controller! nuclear fusion en c!

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24 B I O G RA P H I C A L EMOIRS thus to obtain an inexhaustible source of inexpensive en- ergy. The scientific basis of the scheme, if any, seems to have been the concept of the Boltzmann distribution: Among a large ensemble of atoms in thermal equilibrium there are always a few, at the top of the distribution, that possess the energy required to achieve fusion. The scheme falls into the category of what is nowadays caller! coic! fusion. Richter's only creclentials were an unpublishecl D.Sc. thesis from the German University in Prague, but Peron was fascinated by the scheme en c! approver! its support without any peer re- view. Some German aeronautical engineers hacl just suc- ceeclecl in builcling for Peron an aircraft factory. His cleci- sion to support Richter may have been baser! on the ensuing belief that any project undertaken by Germans is bouncl to be successful: After all, the airplanes flew. After a brief start in his friencl's aircraft factory Richter approached Peron with claims of espionage en cl sabotage en cl the neecl to move his labs to an isolatecl place pro- tectec! by the utmost secrecy. After a search by plane of the most remote areas of the country, Richter cleciclecl to take his lab to Isla Huemul, a beautiful I-square-kilometer is- lanc! in the micicIle of Lake Nahue! Huapi. Peron agrees! and gave Richter full executive powers, as his representative, to run civil en cl professional life on the islancI, en cl on some adjacent areas around! Bariloche, whichever way he saw fit. He moved his lab to Bariloche early in July of 1949, design- ing labs and "reactors" that led to civil engineering works of Pharaonic proportions. In March 1951 Peron set up a press conference in Buenos Aires at which he en cl Richter announced what they cIaimecl to be the first observations of controller! fusion at HuemuT, cletaiTs being cloaked! in secrecy. The details of the conference, as described in a fascinating book by Mariscotti (Mario A. I. Mariscotti, E] Secreto Atomico cle Huemu], Estudio Sigma, Buenos Aires,

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LEOPOLDO MAXIMO FALICOV 25 1996), are strikingly similar to those of the press confer- ence helcl at the University of Utah in 19SOs to announce the discovery of coIcl fusion (Gary Taubes, Bac! Science, the Short Life en c! Weirc! Times of Cocci Fusion, Random House, New York, 1993~. As in the latter case the report of Richter's achievement received wicle international coverage en cl seri- ous en c! concerned! stucly from organizations such as the Atomic Energy Commission in the Unitecl States, which rec- ommenclecl According to the clecIassifiecl minutes of a meet- ing hell! on July 26, 1951) to grant Professor Lyman Spitzer of Princeton $50,000 to perform "research in the area in which Dr. Richter hacl cIaimecl success." As in the case of the Utah coic! fusion 40 years later, once the initial announcement was macle public, clemancis for cletails en cl more visible results grew from clay to clay. Lack of new results, Richter's mismanagement of engineering contracts, en cl Peron's rising clifficulties with the military forcecl the president, adamant to Limit the possibility of a fiasco for which he wouic! have been responsible, to sent! a commission to Bariloche to investigate the facts. The few competent physicists available in Argentina were not to his liking, so he appointee! as members a priest, a naval officer, two engineers (one of them a Berkeley alumnus), en cl a young physicist by the name of lose A. Balseiro, who was doing postdoctoral work in England and was asked to return immecliately to Argentina. The report of the commission was devastating: It recommenclecl immediate closure of Richter's laboratories. After several bizarre incidents Peron reluctantly agreed to send a landing squad to Huemul and to close the labs. This happened on November 22, 1952, a few months after the dramatic cleath of Evita. The total cost of the project has been estimated at U.S.$300 million (tociay's value). Huemul Islancl en cl its builclings became the prop- erty of the military and were used occasionally for target

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26 B I O G RA P H I C A L EMOIRS practice. They were privatizec! a few years ago, en c! are now in the hands of a company that offers excellent guiclecl tours of Richter's installations. It will probably never be known whether Richter was a misguiclec! visionary or a frauclu- lent crook (or a combination thereof). Mounting political unrest from the cleath of Evita until Peron's ouster by the military in 1955 macle the pursuit of scientific activities all but impossible, especially in Buenos Aires. Hence, a few visionary academics conceived the iclea of setting up an elite school of physics in Bariloche, making use of the abanclonecl equipment en cl of the empty builcI- ings on the lakeshore. It was arguccl that talentecl young men graduating from this school wouic! be able to prevent the occurrence of a mishap similar to that of Richter. The negotiations with possible sponsors were long en cl clifficult. Finally classes started in the Argentinean spring of 1955 at about the time of Peron's ouster. Leo joined the first enter- ing class. The first director of the new physics school was Jose A. Balseiro. Bariloche remainec! incleec! insulates! from the ensuing political turmoil, as hacl been hopecl by its founding fathers. (A biography of Balseiro written by two friencis of Leo from his Bariloche clays has recently appeared: A. Lopez Davalos and N. Baldino, J. A. Balseiro: Cronica cle una Ilusion, Fonclo cle Cultura Economica, Buenos Aires, 19991. Balseiro, a gifted physicist with limited research experi- ence, hacl aIreacly proved, as chairman of the Huemul com- mission, to be an excellent administrator. He was able to recruit a competent en cl cleclicatecl faculty, inclucling Spanish mathematicians, German en cl Austrian physicists, Italians, and some of the best Argentinean scientists at hand. To them Leo owocI, by his own admission in the correspon- clence available to us, a great clear of his theoretical train- ing. He gracluatec! in 195S, having obtainer! the maximum

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LEOPOLDO MAXIMO FALICOV 27 gracle of sobresa~iente (outstancling) in the 39 courses he took (a record number for three years!. He must have attracted Balseiro's attention as the brightest of his students en c! a relationship of mutual admiration, respect, en c! friencI- ship clevelopecl between them. The Instituto Balseiro kincIly macle available to us copies of six of the long letters written regularly by Leo to Balseiro in the perioc! from October 1958 (from Cambridge) until April 1961 (from Chicago). They are mostly written in Leo's beautiful handwriting in elegant, flowery Spanish, never forgetting to apologize for the "Ion" silence" since writing his last letter. We also have a copy of one of the answering letters from Balseiro written in June 1961, shortly before his premature cleath in March 1962 at the age of 43 (from leukemia). He is buriecl in a simple grave in front of the institute's library, which now bears the name of Leopoiclo M. FaTicov. In his first letters to his mentor, written after his arrival in Cambridge, Leo points out that harcIly any courses were offerer! there whose contents he was not thoroughly familiar with (thanks to Bariloche). As an exception he mentions Volker Heine's lectures on group theory, which no doubt must have been an important source for the book Leo wrote in Chicago (1966~. He also describes the many seminars he attenclecl on current research topics en cl acicis, "The rest lacks any interest" (this statement should lead to an exercise in humility when react by faculty members of the famous English university). He mentions, however, being very im- pressed by the "hands on" attitude of his English classmates who got involved in current research projects in spite of their insufficient background. He acicis that they were also very impressed by the depth of his knowledge and the edu- cation he hacl received in Bariloche. This en cl some of the letters that followocl expressed his firm desire to return to Bariloche. Later on he begins to wean himself from his

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28 B I O G RA P H I C A L EMOIRS alma mater en c! in his last letter, written from Chicago, he is saciclenecl by the fact that "to the muchachos who now work in Bariloche I must almost be a stranger." Leo's rise through the academic ranks from postcloctoral researcher to full professor at the University of Chicago was rapid. His outstanding scientific achievements cluring this perioc! were matcher! by his teaching. His lectures were extremely clear en cl he was accessible to students who were all impressed by his extraordinary handwriting. His black- boarcis were works of art fillet! with equations involving Arabic, Greek, en cl German script lettering together with diagrams that were cir awn as if rulers were usecI. While on sabbatical leave from Chicago at Cambridge University in 1966, Leo was first approached to consider joining the Berkeley faculty, which he clicl in 1969 as professor of physics. He server! concurrently as a faculty senior scientist en cl principal investigator in the Materials Sciences Division of the Lawrence Berkeley National Laboratory. At Berkeley he continued to produce outstanding research en c! Ph.D. students en cl was a highly regarclecl instructor. In aciclition Leo attracted outstanding postcloctoral researchers. Many who were from South America en c! other Spanish-speaking countries returned home en cl greatly influenced the clevel- opment of physics in their countries. Leo's international connections were vast. He and his wife, Marta, immensely enjoyocl their stays in Denmark. He often travelecl to Europe en cl Asia en cl served on a large number of external evaluation committees. Leo hell! visit- ing positions at more than 20 universities around the worIcI. At Berkeley it was quickly realized that Leo's organiza- tional skills, his rapic! handling of paperwork, en c! his ability to make goocl decisions macle him an icleal cancliciate for committee chairs and faculty administration. When he was chair of the Physics Department ~ ~ 98 I-83), he claimed

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LEOPOLDO MAXIMO FALICOV 29 responsibility for hiring nine new faculty members en c! per- formecl his cluties with unusual speecI. During this period he managed his research group without any decrease in activity. He was almost quantum mechanical seeming to be in "his chairman's office" en cl "his own office" at the same time. When he retired in 1994, he was awarclecl the Berkeley Citation to acknowlecige his high level of service to the university. Leo met his wife, Marta Puebla, on the boat from Buenos Aires to EnglancI. She was going to stucly painting in London, uncler the auspices of the British Council. On the boat they both met Cesar Milstein, a fellow Argentinean en cl British Council scholarship homer, who receiver! the Nobel Prize for medicine in 1984. Leo en cl Marta were married in August 1959. There is one short reference to that event in his cor- responclence with Balseiro. "I have very important private news: Next Thursday, en cl coinciding with the beginning of vacations at the lab, I am getting married en cl shall go for a month to get to know the Continent. My (by now no longer so) future wife has spent a year learning painting in Lonclon . . . she is now in Cambridge preparing herself for her change in civil status." In 1968 Marta gave birth to twin boys, Alexis en cl Ian. Ian's clifficulties in starting to talk lecl to the realization that he was hearing en cl speaking impaired. This handicap receiver! utmost attention from Marta en c! Leo. Their colleagues en cl friends were (ancl still are) most movecl by the acimirable way they managed this handicap en c! how they succeeclec! in communicating with Ian en c! giving him the same type of education Alexis received, avoid- ing special schools en cl colleges. They both attenclecl public schools in Berkeley, any kind of private schools would have meant for Leo en cl Marta betraying their Argentinean prin- ciples of free and lay public education. Both sons attended the University of California at Berkeley, Alexis graduating

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30 B I O G RA P H I C A L EMOIRS with a major in physics en c! Ian in computer science. Ian went on to obtain a master's degree in computer science at the University of California, Santa Cruz, while Alexis obtained a Ph.D. in theoretical physics at MIT. Insteac! of carrying on Leo's torch Alexis then went to meclical school at Harvard, graduating as an M.D. in 1999. Both sons are married en cl have one (Alexis) en c! two (Ian) chiTciren. Alex is an ortho- peclic surgeon working at several hospitals associated with the University of Washington, while Ian works as a computer expert for a private company, Surety, in Reston, Virginia. The label "renaissance man" is overused these clays, but it is an apt description of this unusual man who is sorely missecI. He was a highly skillet! rug weaver, an activity he pursuccl on oIcI-fashionecl looms as a form of relaxation. Leo Falicov's life was rich with art, music, literature, en cl hobbies. Leo courter! his Marta by reciting from Pablo Nerucia en cl Garcia Lorca, while sitting by a river in Cambridge, EnglancI. He lovecl the opera. He couIcl recite poetry en cl quote literature in three languages. He collected! art en c! playocl the piano. His sense of humor en cl wry stories macle him a favorite dinner companion. He is fancily remembered as a vibrant incliviclual en c! brilliant scholar from whom his family, friends, colleagues, en cl students clerivecl love en cl support.

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LEOPOLDO MAXIMO FALICOV SELECTED PUBLICATIONS 1960 31 The theory of photon packets and the Lennuier effect. Nuovo Cimento 16:247. With M. H. Cohen. Effect of spin-orbit splitting on the Fermi sur- face of the hexagonal close packed metals. Phys. Rev. Lett. 5:544. 1961 With M. H. Cohen. Magnetic breakdown in crystals. Phys. Rev. Lett. 7:231. 1962 The band structure and Fermi surface of magnesium. Philos. Trans. R. Soc. Lond. A 255:55. With M. H. Cohen and J. C. Phillips. Superconductive tunneling. Phys. Rev. Lett. 8:316. 1963 With M. H. Cohen. Spin-orbit coupling in the band structure of magnesium and other hexagonal-close-packed metals. Phys. Rev. 130:92. With M. G. Priestley and G. Weisz. Experimental and theoretical study of magnetic breakdown in magnesium. Phys. Rev. 191:616. 1964 With D. H. Douglass, Jr. The superconductive energy gap. In Progress in Low Temperature Physics, vol. IV, ed. C. }. Gorter, p.97. Amsterdam: North Holland. With P. Sievert. Magnetoresistance and magnetic breakdown. Phys. Rev. Lett. 12:558. 1966 With P. J. Lin. Fermi surface of arsenic. Phys. Rev. 142:441. Group Theory and Its Physical Applications. Chicago: University of Chicago Press.

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32 B I O G RA P H I C A L 1967 EMOIRS With R. W. Stark. Magnetic breakdown in metals. In Low Temperature Physics, vol. V, ed. C. J. Gorter, p. 235. Amsterdam: North Holland. 1968 With P. B. Allen, M. L. Cohen, and R. V. Kasowski. Superconductivity and band structure from a single pseudopotential: Zinc and cadmium. Phys. Rev. Lett. 21:1794. 1970 With R. Ramirez and J. C. Kimball. Metal-insulator transitions: A simple theoretical model. Phys. Rev. B 2:3383. 1973 With P. Y. Yu, Y. R. Shen, and Y. Petroff. Resonance Raman scatter- ing at the forbidden yellow excitor in Cu2O. Phys. Rev. Lett. 30:283. 1975 With B. Koiller. Low temperature conductivity of transition-metal oxides. 7. Solid State Chem. 12:349. With F. Yndurain. Model calculation of the electronic structure of a (111) surface in a diamond-structure solid. 7. Phys. C: Solid State Phys. 8:147. With F. Yndurain. New theory of binary alloys with short-range order properties. Solid State Commun. 17:1545. 1977 With C. Guillot, Y. Ballu, J. Paigne, J. Lecante, K. P. lain, P. Thiry, R. Pinchaux, and Y. Petroff. Resonant photoemission in nickel metal. Phys. Rev. Lett. 39:1632. 1980 With E. E. Haller and B. loos. Acceptor complexes in germanium: Systems with tunneling hydrogen. Phys. Rev. B 21:4729. 1986 With J. M. Kahn and E. E. Haller. Isotope-induced symmetry change in dynamic semiconductor defects. Phys. Rev. Lett. 57:2077.

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LEOPOLDO MAXIMO FALICOV 33 1 989 With D. C. Chrzan. Exactly soluble model for antiphase boundaries in binary ordering alloys. Phys. Rev. B 40:8194. 1991 With H.-A. Lu, C. G. Slough, R. V. Coleman, and A. Maiti. Meta- stable charge density-wave states in NbSe3 studied by magneto- transport. Phys. Rev. B 44:6037. 1992 With J. K. Freericks. Heavy-fermion systems in magnetic fields: The metamagnetic transition. Phys. Rev. B 46:874. 1994 With R. Q. Hood. Theory of the negative magnetoresistance of ferromagnetic-normal metallic multilayers. 7. Appl. Phys. 76:6595.