Beautifully strange - The Strangest Man: The Hidden Life of Paul Dirac, Quantum Genius

The list of famous Bristolians is an illustrious one. The Victorian engineer Isambard Kingdom Brunel, for example, is recognized everywhere in Bristol for his many iconic structures, even though he was not born, bred or even resident in the city. Another well-known son of the city is the Hollywood legend Cary Grant, born as Archie Leach in the suburb of Horfield and now commemorated with a striking bronze statue outside Bristol’s hands-on science museum. The physicist Paul Dirac actually went to the same elementary school as Grant/ Leach, and the abstract sculpture dedicated to him stands just a stone’s throw away from Grant’s bronze likeness. Dirac also has a building named after him: Dirac House, the headquarters of IOP Publishing (which publishes Physics World).

Yet in spite of these efforts to publicize Dirac’s many contributions to science, his city of birth and (until recently) the school where he was educated seemed almost unaware that in Dirac, Bristol produced one of the great minds of the last century, and arguably the greatest British physicist since Isaac Newton. Part of this lack of knowledge among both Bristolians and the general public is Dirac’s legendary reticence, literal-mindedness and almost total inability to communicate with anyone — except, possibly, his immediate family.

All of this makes Dirac a very difficult subject for the sort of sympathetic biography that Graham Farmelo has produced in The Strangest Man: The Hidden Life of Paul Dirac, Quantum Genius. The book represents years of careful research and conversations with family and friends who knew Dirac and his work. In it, Farmelo, a science communicator and senior research fellow at the London Science Museum, describes the life and work of this profoundly brilliant man, exploring the origins of his near-pathological reticence and in the last chapter proposing a possible explanation. I doubt whether a better biography will appear in most of our lifetimes.

Dirac’s parents Charles and Florence were married in 1899 and lived for a time at 42 Cotham Road, probably in rented rooms, where Dirac’s older brother Felix was born. Shortly afterwards, Charles bought a small terraced house in Monk Road and Paul Adrien Maurice Dirac, the second son, was born in 1902. His sister Betty was born in 1906, so Flo certainly had her hands full with a young family and the ever-increasing and apparently irrational demands of her husband.

These demands included Charles’ insistence that only French be spoken at the family dining table. As a result, Flo, Felix and Betty ate in the kitchen, while Paul — whose French was just passable — was allowed to sit with his Swiss-born father. In later life, Dirac acknowledged that his difficulty in communicating with others may have stemmed from this period, poignantly explaining to Kurt Hofer — an Austrian- born cell biologist who became a close friend — that “since I found that I couldn’t express myself in French, it was better for me to stay silent than to talk in English”.

Time and again, Farmelo returns to the difficult personal relations that plagued Dirac’s family. Although in today’s parlance the Diracs were upwardly mobile — they soon moved to a larger semi-detached house in Julius Road, a more salubrious part of Bristol — Charles was also a serial tax evader. His crimes only came to light after his death, however, leaving Flo with an unwelcome tax bill. At one stage in the relationship she appears to have sought separation from her husband due to suggestions that he was having an extramarital affair, and their oldest child Felix committed suicide when Dirac was 23. But despite all of these traumas, Dirac is said to have wept only once in his life: in 1955, when he heard of the death of his hero, Einstein.

Given this background, it is hardly surprising that in his later life it was only with some unhappiness and after pleading from his mother that Dirac could be persuaded to visit Bristol. Instead, St John’s College, Cambridge, became the place he regarded as his true home. While there, Dirac made his most important breakthrough: he succeeded in welding together special relativity and quantum mechanics to produce what is often and rightly regarded as one of the great equations in physics. He became the Lucasian Professor of Mathematics there in 1932, and in 1933 his famous equation won him a Nobel prize (shared with Schrödinger) “for the discovery of new productive forms of atomic theory”.

Master of the equation: Paul Dirac.

Credit: Science Source/Science Photo Library

The conclusions of the Dirac equation were highly controversial when they were first described in 1928, but in a curious way, the criticisms appeared to simply bounce off Dirac — a consequence, perhaps, of his deeply private personality. The idea of negative energy states and the consequent hole theory was finally resolved by the discovery of the positron in 1932. The equation also showed that spin was a natural consequence of relativity and quantum mechanics, and not simply an add-on to explain atomic spectra. Recognizing this, it is only just and fair that the unique characteristics of electrons that make such devices as transistors, mobile phones and solid-state lasers possible are known as Fermi–Dirac statistics.

Farmelo takes the reader through difficult physics in a masterly manner — a consequence, no doubt, of his vast experience in science communication. The author also describes some aspects of Dirac’s work of which even professional physicists may not be aware. For example, in 1933 Dirac started an experimental study with Peter Kapitza on the possibility of bending a beam of electrons with light. He also developed an experiment to separate isotopes — much to the approval of Ernest Rutherford, who thought that it “augurs well for theoretical physics that the Lucasian Professor is soiling his hands in the laboratory”. As a result, Dirac became peripherally involved in the Manhattan Project, performing theoretical investigations of the “separation power” of uranium-enriching devices, although he declined a fulltime position.

Dirac’s life changed dramatically during a sabbatical at Princeton University in 1934 when he met Margit Wigner, a Hungarian divorcee and mother of two children, Gabriel and Judy. Margit, the sister of nuclear physicist Eugene Wigner, was known to friends and family as Manci. She was the opposite in nearly every sense to Dirac, but their affection turned to love and they were married in January 1937. Manci had to spend some time in Budapest after the honeymoon and as a result, Dirac penned “the first love letter I have ever written”. Until then, Dirac had replied to questions from Manci in tabular form!

The marriage did experience some strains (often arising from Manci’s dislike of Cambridge), but Dirac was a loving husband and stepfather to Manci’s children and to the two daughters of the marriage, Mary and Monica. Within the family, Dirac appears to have been far more communicative than he was with outsiders. At the opening of Dirac House in 1997, I remember Monica describing how his scientific approach to vegetable gardening caused much amusement in the family, which Dirac took in good humour.

One feels a sense of anticlimax as the book nears its end. Dirac fell out with the Cambridge hierarchy over what seems a rather trivial dispute about car parking, and by the mid- 1960s he spent most of the week working at home. Meanwhile, Manci had set her heart on escaping from Cambridge, and in 1971, having seen their children well settled (except for Dirac’s stepdaughter Judy, who had disappeared in 1968 and was by then presumed to be dead), the couple finally emigrated from the UK to Florida, where Dirac died in 1984.

Physicists remain divided over the legacy of Dirac’s later years. Was his opposition to the success of quantum electrodynamics justified on the grounds that the theory lacked beauty? Do monopoles really exist? Can his large-number hypothesis — which suggests that fundamental constants change with time — ever be reconciled with general relativity? But all physicists agree that the towering achievement of the Dirac equation will, as Farmelo makes clear, set Dirac apart and place him in a league with Newton and Einstein.

Perhaps the most controversial part of the book is its last chapter, in which Farmelo explores the possibility that Dirac’s pathological reticence was in fact undiagnosed autism or Asperger’s syndrome. Autism covers a wide spectrum of behaviour, and as the writer and doctor Milo Keynes points out in The Notes and Records of the Royal Society (2008 62 289), it has become something of a catch-all phrase for behaviour that departs significantly from the norm: “In the past 10 years it has been firmly claimed that Newton must have shown the development disorder of Asperger’s syndrome, a disorder that has been posthumously assigned to Michelangelo, Henry Cavendish, Albert Einstein, Marie Curie, Ludwig Wittgenstein and Paul Dirac.” Clearly, Dirac joins a long and distinguished list of retrospectively diagnosed luminaries.

For what it is worth, my guess is that Dirac was by nature a shy individual and that this shyness was reinforced by a difficult early home environment. Farmelo is correctly very cautious in what he has written, and regardless of the conclusions he draws about Dirac’s personality, it is clear that writing about him has been a labour of love. I most warmly recommend this book both to professional physicists and to laypersons interested in fundamental physics, as well as to anyone who finds the interaction between personality and intellectual endeavour fascinating.
About the author

FONTE: PhysicsWorld
Sir John Enderby is professor emeritus of physics at Bristol University and past president of the Institute of Physics

Journeys to greatness

To practising physicists, the great equations of physics might seem obvious, logical and trivial. But to their discoverers, Robert P Crease argues, that was far from true

Readers, I hope, will forgive me for a shameless bit of self-publicity about my latest book, The Great Equations: Breakthroughs in Science from Pythagoras to Heisenberg (Norton). But then the book is partly yours too, inspired as it was by the responses of Physics World readers to my request for suggestions of great equations (see “Critical Point: The greatest equations ever”). In the book, I chose to discuss not the most frequently mentioned equations, but those that seem to have engaged their discoverers in the most remarkable journeys.

The journey metaphor may seem misleading if taken to suggest smooth and steady progress to an already known destination. The scientific journeys I recount — which include those culminating in F=ma, and the equations of Maxwell and Schrödinger — were unpredicted, often protracted and erratic. The journey metaphor should also not imply that the travellers passively observed the changing scenery; in fact, the scientists interacted with their environment while altering it.

But the journey metaphor does capture one important aspect of the birth of these equations, which is how their originators’ ideas about what was important changed during the course of their research. Newton, Maxwell, Schrödinger and others each inherited a “landscape” or view of how knowledge about nature was organized. But during their research, new concepts — such as mass and force, entropy and displacement current, quanta and wave equations — appeared on the horizon, grew in importance and displaced others to assume positions as indispensable landmarks in the conceptual landscape.

For the ultimate destination of such scientists was not a particular location that they saw beforehand, but clarity. They were dissatisfied with what they had, perceived a vision of what might take its place, and were able to carry out the inquiry needed to realize it. At each step, they found the world to be somewhat discordant — not fully grasped — with hints of another, deeper order just over the horizon. This discordance is what makes newly realized equations seem, strangely, to be both discovered and invented.

Oliver Heaviside, who transformed Maxwell’s then-convoluted equations into their now-familiar versions, once remarked that “it was only by changing its form of presentation that I was able to see it [electromagnetism] clearly”. The sense of that remark — you transform to clarify — could have been said by any of the scientists mentioned in The Great Equations.

No royal road

Most of the time we are less interested in journeys than in where they take us. But we can learn much from them. One is just how varied such journeys are. Sometimes they are taken by scientists who talk and argue constantly with one another, as with the equations of thermodynamics and the uncertainty principle. Other journeys were undertaken by individuals working essentially by themselves, such as Einstein in his path to general relativity and Schrödinger to his wave equation, though such individuals in effect carried on conversations with colleagues even when working alone. There is no royal road to discovery.

Another thing we learn is that equations are not simply inert tools that work only in the hands of scientists and engineers. They can also exert an educational and even cultural force that shapes our view of the world. The Pythagorean theorem teaches us what proof means, the second law of thermodynamics keeps in check our dreams of free energy, Einstein’s equations changed our understanding of space and time, and the work of Schrödinger and Heisenberg forces us to rethink what being a “thing” means.

We also learn to appreciate how deeply affecting the scientific life can be. The scientists who took those journeys were never blasé, never disinterested. They were infused with curiosity, consternation, bafflement, frustration and wonder. And each scientist had what might be called a particular style. Some succeeded because they were only satisfied when they found what they were looking for, while others succeeded only because they were prepared to see something more than they expected.

Most of all, the journeys allow us to glimpse the mutability of nature and our role in it. The journeys teach us that nature could be otherwise — that it was otherwise for us until a moment ago, and for all we know it could change in the future. In such instances, we experience a transcendent moment in which a higher thought emerges in the middle of an existing one.

The critical point

The Great Equations ends by relating a conversation I had while writing the book, with an elderly physicist who expressed little comprehension and sympathy. To his workmanlike mind, the equations I mentioned seemed so obvious and logical that he could not picture not having known them, and he saw no value in making them more enigmatic. “Such equations”, he told me, “would not be wonderful if people realized how trivial they are. You should help them do so.”

I could have hugged him. At that moment, I finally realized exactly what I was trying to do. It was exactly the opposite — to undo that sense of obviousness and triviality, and to take readers back to the moment just before the equations were discovered, to appreciate how untrivial they are. Readers could, I hoped, thereby relive the wonder of the moment when the equations were first grasped — when they seemed simultaneously discovered and invented.

Scientists such as my physicist acquaintance tend to focus on the formal, discovered — what he meant by “trivial” — aspect of the birth of equations, whereas philosophers and historians tend to focus on the other aspect, having to do with their invention. It ought to be possible, I felt, to capture both aspects at once — which would, I thought, finally provide a more complete picture of the discovery process itself.

About the author

Robert P Crease is chairman of the Department of Philosophy, Stony Brook University, and historian at the Brookhaven National Laboratory, US

Fonte: PhysicsWorld

Concurso para físico da usina nuclear de Angra dos Reis

http://www.fesp.rj.gov.br/fesp_2007/concursos/eletronuclear1/paginaeletronuclear1.asp




FÍSICO(A) - CONHECIMENTOS ESPECÍFICOS



Física Geral, Mecânica Clássica e Relatividade, Mecânica Quântica, Eletromagnetismo, Termodinâmica e Física Estatística, Princípios de Física Atômica, Molecular e Ótica, Física dos Sólidos, Princípios de Física Nuclear, Princípios gerais de Proteção Radiológica.



Sugestões Bibliográficas:



B.H. Bransden e C.J. Joachain, Physics of Atoms and Molecules, 2nd. Ed., Pearson Education Limited, UK, 2003

C. Cohen-Tannoudji, B. Diu e F. Laloe, Quantum Mechanics, (X) ed. Ed. Wiley-Interscience, New Jersey, 1977.

C. Kittel e H. Kroemer, Thermal Physics, 2a ed. Ed. W. H. Freeman, New York, 1980.

C. Kittel, Introduction to Solid State Physics, 8a. ed. Ed. J. Wiley & Sons, New York, 2005.

D. J. Griffiths, Introduction to Electrodynamics, 3a ed. Ed. Prentice-Hall, New Jersey, 1999.

D. P. Menezes, Introdução à Física Nuclear e de Partículas Elementares, Ed. UFSC, Florianópolis, 2002

F. H. Attix, Introduction to Radiological Physics and Radiation Dosimetry. Ed. J. Wiley & Sons, New York, 1986.

H. Goldstein, Classical mechanics, 2a ed. Ed. Addison-Wesley, Reading, 1980.

H. M. Nussenzveig, Curso de Física Básica (volumes 1 a 4), 2a ed, Ed. Edgard Blücher LTDA, São Paulo, 1995.

J. D. Jackson, Classical Electrodynamics, 3a ed. Ed. J. Wiley & Sons, New York, 1998.

K. C Chung, Introdução à Física Nuclear, Ed. UERJ, Rio de Janeiro, 2001.

K. R. Symon, Mechanics, 3a ed. Ed. Addison-Wesley, Reading, 1971.

N. W. Ashcroft e N. D. Mermin, Solid State Physics, (X) ed. Ed. Saunders College, Philadelphia, 1976.

P. A. Tipler, Física para cientistas e engenheiros, Volume 4: Ótica e física moderna. 3a ed. Ed. Guanabara Koogan, Rio de Janeiro, 1994.

R. Reif, Fundamentals of Statistical and Thermal Physics, 1a ed. Ed. McGraw-Hill, New York, 1965.

S. Gasiorowicz, Física Quântica, 3a ed. Ed. Guanabara Dois, Rio de Janeiro, 1979.



FÍSICO(A) - BLINDAGEM E PROTEÇÃO RADIOLÓGICA - CONHECIMENTOS ESPECÍFICOS



Física Geral, Mecânica Clássica e Relatividade, Mecânica Quântica, Eletromagnetismo, Termodinâmica e Física Estatística, Princípios de Física Atômica, Molecular e Ótica, Física dos Sólidos, Princípios de Física Nuclear, Proteção Radiológica e Blindagem Convencional, incluindo: radiação ionizante, grandezas dosimétricas e radiológicas, atenuação exponencial, HVL, TVL. equilíbrio de radiação e partículas carregadas, dose absorvida, decaimento radioativo, interações entre fótons e matéria, produção e qualidade de raios-X, teoria da cavidade, fundamentos de dosimetria, interações e dosimetria de nêutrons.



Sugestões Bibliográficas:



B.H. Bransden e C.J. Joachain, Physics of Atoms and Molecules, 2nd. Ed., Pearson Education Limited, UK, 2003

C. Cohen-Tannoudji, B. Diu e F. Laloe, Quantum Mechanics, (X) ed. Ed. Wiley-Interscience, New Jersey, 1977.

C. Kittel e H. Kroemer, Thermal Physics, 2a ed. Ed. W. H. Freeman, New York, 1980.

C. Kittel, Introduction to Solid State Physics, 8a. ed. Ed. J. Wiley & Sons, New York, 2005.

D. J. Griffiths, Introduction to Electrodynamics, 3a ed. Ed. Prentice-Hall, New Jersey, 1999.

D. P. Menezes, Introdução à Física Nuclear e de Partículas Elementares, Ed. UFSC, Florianópolis, 2002

F. H. Attix, Introduction to Radiological Physics and Radiation Dosimetry. Ed. J. Wiley & Sons, New York, 1986.

H. Goldstein, Classical mechanics, 2a ed. Ed. Addison-Wesley, Reading, 1980.

H. M. Nussenzveig, Curso de Física Básica (volumes 1 a 4), 2a ed, Ed. Edgard Blücher LTDA, São Paulo, 1995.

J. D. Jackson, Classical Electrodynamics, 3a ed. Ed. J. Wiley & Sons, New York, 1998.

K. C Chung, Introdução à Física Nuclear, Ed. UERJ, Rio de Janeiro, 2001.

K. R. Symon, Mechanics, 3a ed. Ed. Addison-Wesley, Reading, 1971.

N. W. Ashcroft e N. D. Mermin, Solid State Physics, (X) ed. Ed. Saunders College, Philadelphia, 1976.

P. A. Tipler, Física para cientistas e engenheiros, Volume 4: Ótica e física moderna. 3a ed. Ed. Guanabara Koogan, Rio de Janeiro, 1994.

R. Reif, Fundamentals of Statistical and Thermal Physics, 1a ed. Ed. McGraw-Hill, New York, 1965.

S. Gasiorowicz, Física Quântica, 3a ed. Ed. Guanabara Dois, Rio de Janeiro, 1979.



FÍSICO(A) - NUCLEAR: FÍSICA DE REATORES - CONHECIMENTOS ESPECÍFICOS



Características termohidráulicas dos vários tipos de reatores nucleares: PWR, BWR, LMFBR, HTGR. Propriedades dos materiais usados em reatores nucleares. Princípios de projeto térmico do reator. Limitações no projeto termohidráulico. Geração de calor no reator, DNBR, fator de pico de potência, fator de canal quente. Termodinâmica de sistemas nucleares, ciclos de Rankine simples e complexo, ciclos de Brayton simples e complexo, ciclo combinado. Condução de calor nos elementos combustíveis. Distribuição de temperatura no combustível, revestimento e refrigerante. Escoamentos monofásico e bifásico. Transferência de calor monofásica para o refrigerante. Transferência de calor com mudança de fase. Termohidráulica simples do núcleo. Análise termohidráulica monofásica de um canal aquecido.



Sugestões Bibliográficas:



N.E. Todreas e M.S. Kazimi, Nuclear Systems: Vol. I, Thermal Hydraulic

Fundamentals, Hemisphere, New York, 1990.

J.H. Rust, Nuclear Power Plant Engineering, Haralson, Buchanan, Georgia, 1979.

M.M. El-Wakil, Nuclear Heat Transport, International Textbook Co., Scranton,

Pennsylvania, 1971.



FÍSICO(A) – TREINAMENTO - CONHECIMENTOS ESPECÍFICOS



Física Geral, Mecânica Clássica e Relatividade, Mecânica Quântica, Eletromagnetismo, Termodinâmica e Física Estatística, Princípios de Física Atômica, Molecular e Ótica, Física dos Sólidos, Princípios de Física Nuclear, Princípios gerais de Proteção Radiológica. Uma fração da prova dará ênfase à compreensão e explicação simples de fenômenos físicos, e à assimilação de novos conceitos à partir da base acima e sua tradução e interpretação a uma linguagem simples.



Sugestões Bibliográficas:



H. M. Nussenzveig, Curso de Física Básica (volumes 1 a 4), 2a ed, Ed. Edgard Blücher LTDA, São Paulo, 1995.

P. A. Tipler, Física para cientistas e engenheiros, Volume 4: Ótica e física moderna. 3a ed. Ed. Guanabara Koogan, Rio de Janeiro, 1994.

H. Goldstein, Classical mechanics, 2a ed. Ed. Addison-Wesley, Reading, 1980.

K. R. Symon, Mechanics, 3a ed. Ed. Addison-Wesley, Reading, 1971.

J. D. Jackson, Classical Electrodynamics, 3a ed. Ed. J. Wiley & Sons, New York, 1998.

D. J. Griffiths, Introduction to Electrodynamics, 3a ed. Ed. Prentice-Hall, New Jersey, 1999.

R. Reif, Fundamentals of Statistical and Thermal Physics, 1a ed. Ed. McGraw-Hill, New York, 1965.

C. Kittel e H. Kroemer, Thermal Physics, 2a ed. Ed. W. H. Freeman, New York, 1980.

C. Kittel, Introduction to Solid State Physics, 8a. ed. Ed. J. Wiley & Sons, New York, 2005.

N. W. Ashcroft e N. D. Mermin, Solid State Physics, (X) ed. Ed. Saunders College, Philadelphia, 1976.

C. Cohen-Tannoudji, B. Diu e F. Laloe, Quantum Mechanics, (X) ed. Ed. Wiley-Interscience, New Jersey, 1977.

S. Gasiorowicz, Física Quântica, 3a ed. Ed. Guanabara Dois, Rio de Janeiro, 1979.

B.H. Bransden e C.J. Joachain, Physics of Atoms and Molecules, 2nd. Ed., Pearson Education Limited, UK, 2003

K. C Chung, Introdução à Física Nuclear, Ed. UERJ, Rio de Janeiro, 2001.

D. P. Menezes, Introdução à Física Nuclear e de Partículas Elementares, Ed. UFSC, Florianópolis, 2002

F. H. Attix, Introduction to Radiological Physics and Radiation Dosimetry. Ed. J. Wiley & Sons, New York, 1986.



FÍSICO(A) – ANÁLISE PROBABILÍSTICA DE SEGURANÇA - CONHECIMENTOS ESPECÍFICOS



Física Geral, Mecânica Clássica e Relatividade, Mecânica Quântica, Eletromagnetismo, Termodinâmica e Física Estatística, Princípios de Física Atômica, Molecular e Ótica, Física dos Sólidos, Princípios de Física Nuclear, Princípios gerais de Proteção Radiológica. Uma fração da prova dará ênfase à construção de modelos à partir da base de conhecimentos acima; além de ênfase em Probabilidade e Estatística.



Sugestões Bibliográficas:



H. M. Nussenzveig, Curso de Física Básica (volumes 1 a 4), 2a ed, Ed. Edgard Blücher LTDA, São Paulo, 1995.

P. A. Tipler, Física para cientistas e engenheiros, Volume 4: Ótica e física moderna. 3a ed. Ed. Guanabara Koogan, Rio de Janeiro, 1994.

H. Goldstein, Classical mechanics, 2a ed. Ed. Addison-Wesley, Reading, 1980.

K. R. Symon, Mechanics, 3a ed. Ed. Addison-Wesley, Reading, 1971.

J. D. Jackson, Classical Electrodynamics, 3a ed. Ed. J. Wiley & Sons, New York, 1998.

D. J. Griffiths, Introduction to Electrodynamics, 3a ed. Ed. Prentice-Hall, New Jersey, 1999.

R. Reif, Fundamentals of Statistical and Thermal Physics, 1a ed. Ed. McGraw-Hill, New York, 1965.

C. Kittel e H. Kroemer, Thermal Physics, 2a ed. Ed. W. H. Freeman, New York, 1980.

C. Kittel, Introduction to Solid State Physics, 8a. ed. Ed. J. Wiley & Sons, New York, 2005.

N. W. Ashcroft e N. D. Mermin, Solid State Physics, (X) ed. Ed. Saunders College, Philadelphia, 1976.

C. Cohen-Tannoudji, B. Diu e F. Laloe, Quantum Mechanics, (X) ed. Ed. Wiley-Interscience, New Jersey, 1977.

S. Gasiorowicz, Física Quântica, 3a ed. Ed. Guanabara Dois, Rio de Janeiro, 1979.

B.H. Bransden e C.J. Joachain, Physics of Atoms and Molecules, 2nd. Ed., Pearson Education Limited, UK, 2003

K. C Chung, Introdução à Física Nuclear, Ed. UERJ, Rio de Janeiro, 2001.

D. P. Menezes, Introdução à Física Nuclear e de Partículas Elementares, Ed. UFSC, Florianópolis, 2002

F. H. Attix, Introduction to Radiological Physics and Radiation Dosimetry. Ed. J. Wiley & Sons, New York, 1986.

Spintrônica abre novos rumos ao associar a carga dos elétrons à sua rotação

Muita gente fissurada em tecnologia ouve falar em spintrônica mas não sabe direito o que é. Parece até coisa do futuro. Mas quando ligamos nosso computador e o disco rígido começa a girar lá dentro mal podemos imaginar que nesse dispositivo a spintrônica já é aplicada há um bom tempo.

Essa ciência permitiu literalmente diminuir o tamanho físico do bit gravado na superfície metálica do disco, possibilitando um aumento brutal na densidade de informações gravadas.

A dra. Tatiana Rappoport, professora da UFRJ com doutorado em Física, explica que a spintrônica já participa da nossa realidade tecnológica há mais ou menos uns dez anos.

- Cerca de 95% dos discos rígidos hoje no mercado já utilizam essa tecnologia. Mas a spintrônica é uma ciência repleta de futuras aplicações, quase todas fascinantes - disse. - Só para se ter idéia da sua importância, os dois físicos que ganharam o Nobel recentemente, Albert Fert e Peter Grünberg, foram os precursores da spintrônica, com seus estudos sobre magneto-resistência gigante.

Para explicar de forma simples o que é spintrônica, Tatiana lembra que, enquanto no disco rígido os bits são magnéticos, na placa-mãe eles são eletricidade, ou seja, valem "1" quando passa corrente elétrica e valem "0" quando não passa.

- A spintrônica é a eletrônica mesclada com magnetismo, ou seja, magnetoeletrônica. É uma ciência que leva em conta que os elétrons giram e, por isso, têm um campo magnético associado. Essa rotação dos elétrons é o chamado "spin", termo inglês que significa girar - esclarece. - Além da miniaturização, outra aplicação da spintrônica é permitir um menor consumo de energia em dispositivos eletrônicos.

O objetivo futuro dessa ciência ciência emergente é mesclar dois mundos, o da eletricidade e o do magnetismo. Mais especificamente, permitir o controle elétrico das propriedades magnéticas de um material e, reciprocamente, possibilitar o controle magnético das propriedades elétricas desse mesmo material.

A densidade de informações nos HDs só não é maior porque a spintrônica por ora só é aplicável à leitura dos dados gravados. Para gravar informações no disco, por enquanto, o jeito é usar a moda antiga, ou seja, indução elétrica - uma bobina imprime a magnetização do bit no metal do disco girante.

- Mas já existem várias possibilidades científicas sendo estudadas com o intuito de escrever de forma mais precisa em HDs, aumentando a resolução dos bits gravados no metal - explica Tatiana. - Um desses filões de pesquisa é o chamado STT (spin torque transfer), ou transferência por de spin.

Os chips convencionais que estávamos acostumados a ver, tais como SRAMs (memória de acesso aleatório estático) e DRAMs (memória de acesso aleatório dinâmico) perdiam as informações armazenadas caso se desligasse a eletricidade. Para resolver essa chateação, foram criadas MRAMs, memórias magnéticas de acesso aleatório, em que os dados digitais não são gravados eletricamente mas sim por magnetismo. Ou seja, pode-se desligar a força e a memória não se apaga.

A geração mais recente das MRAMs usa o efeito de torque de spin para programar os bits numéricos. Com um pequeno pulso de corrente elétrica é possível programar o estado de memória da célula magnética, o que representa uma vitória naquele objetivo de reciprocidade - usar magnetismo para controlar a eletricidade e, no caso, usar eletricidade para controlar o magnetismo.

Uma coisa que ainda atrapalhava um pouco a viabilidade dessas memórias era a demora na magnetização -- 10 nanossegundos para fazer uma gravação. Parece pouco, mas não é. No entanto, recentes pesquisas realizadas na Alemanha usando um efeito chamado "reversão balística de magnetização por torque de spin" conseguiu reduzir esse tempo para apenas 1 nanossegundo. Assim, espera-se que, em breve, memórias MRAM serão quase tão rápidas quanto as antigas SRAMs e DRAMs. Com relação aos discos rígidos, essa mesma técnica de toque de spin permitirá gravar informações mais densas neles.

Em termos de mercado, as aplicações da spintrônica têm sido em metais, como é o caso dos discos rígidos. Daqui para a frente, porém, o grande lance será a spintrônica em semicondutores, que abrirá um leque surpreendente de novas aplicações, incluindo o tão sonhado computador quântico.

Embora ainda um pouco longe de ser implementado, o computador quântico terá como grande vantagem a altíssima velocidade de processamento, permitindo resolver problemas altamente complexos, tais como criptografia, fatoração de números primos, pesquisa de informação em bancos de dados não ordenados etc.

- Talvez a primeira implementação do computador quântico seja algo envolvendo spintrônica e optoeletrônica, ou seja, circuitos envolvendo magnetismo (spin), fótons (luz = óptica) e elétrons (eletricidade) - devaneia a cientista.

Um dos primeiros passos rumo ao computador quântico foi a obtenção do bit quântico, ou qubit, em que um único elétron é isolado e o sentido de seu spin (rotação) determina seu valor zero ou um. Com dois qubits pode-se construir com apenas dois elétrons uma .

- O qubit não é o elétron em si, mas sim o spin do elétron - esclarece Tatiana.

Algumas experiências recentes com qubits foram feitas em filmes finos de material semicondutor em que os elétrons só podem se mover num plano, ou seja, em duas dimensões.

" Usando condutores de ouro e certas voltagens, a gente obriga um elétron a ficar confinado num único ponto, e com spin definido "

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- Usando condutores de ouro e certas voltagens, a gente obriga um elétron a ficar confinado num único ponto, e com spin definido - afirma a cientista. - Já se domina todo o processo de manipulação de spin de um elétron assim confinado. Em 2007 foi a primeira vez que os nossos colegas conseguiram fazer a última coisa que faltava, ou seja, efetuar o giro o spin.

Ao explicar esses conceitos e outros ainda mais complexos e virtualmente impublicáveis aqui na nossa Revista Digital, Tatiana vibra e se entusiasma, entre slides herméticos e vídeos cabeludíssimos. Ela foi entrevistada no Laboratório de Semicondutores da PUC-Rio, onde, entre diversas outras atividades, fabrica-se semicondutores específicos para as pesquisas em andamento. Uma vez prontos, esses semicondutores, lá mesmo na PUC, eles são avaliados em suas características ópticas e elétricas.

- A caracterização magnética nós fazemos na UFRJ, lá no Fundão, onde temos um laboratório específico para essa finalidade - explica a pesquisadora.

Tatiana recebeu em 2006 menção honrosa no Programa de Bolsas Estudo para Jovens Cientistas oferecido em parceria por L'Oréal, UNESCO e Academia Brasileira de Ciências. Mas o melhor lhe aconteceu no ano seguinte, quando foi uma das sete jovens mulheres cientistas laureadas no Brasil, recebendo um prêmio de US$ 20 mil por sua pesquisa sobre manipulação de spins e cargas.

Tatiana vive e respira Física. E explica essa ciência complicada com a leveza de que está contando um caso. Talvez não à toa, ela se casou com um físico. Tatiana é adepta ferrenha de Linux e de sistemas abertos em geral e, quando escolheu adquirir seu laptop Mac, que já tem cinco anos de uso, teve lá seus motivos.

- Por trás dessa maravilha o que roda é na verdade um BSD [o UNIX de Berkeley] embelezado - esclarece. - Mas preciso mesmo é comprar um notebook novo, e ele também vai ser um Mac, é claro.

A o site da pesquisadora possui muitas aulas em PDFs, clqiue AQUI!

Fonte: O GLOBO - Publicada em 27/10/2008 por Carlos Alberto Teixeira