- Person
- Felix Bloch
- Lived
- 1905–1983
- Field
- Physics
- From
- Swiss-American
The story
Felix Bloch was born in Zurich in 1905 to a Jewish family. He entered the Federal Institute of Technology in Zurich intending to become an engineer, but after a year he switched to physics, attending courses by Peter Debye, Hermann Weyl and Erwin Schrödinger just as the new wave mechanics was being born. In 1927, on Debye's advice, he moved to the University of Leipzig and became Werner Heisenberg's first graduate student.
Heisenberg suggested a thesis topic that had baffled some of the best physicists of the age, including Drude, Lorentz, Pauli and Sommerfeld: the conductivity of metals. Earlier theories worked only by treating the conduction electrons as a free gas, and no one understood why that should be allowed. Bloch saw the central question as how electrons could slip past all the ions of a metal instead of colliding with them at every atomic distance.
To make the problem manageable, he began with electrons in a one-dimensional repeating potential. Using Fourier analysis, he found that the electron's wave differed from that of a free electron only by a periodic modulation that repeats with the lattice. He thought it too simple to be much of a discovery, but when he showed it to Heisenberg, his teacher replied at once that this was it. Bloch completed the work in the summer of 1928, and his thesis on the quantum mechanics of electrons in crystal lattices was published in the Zeitschrift für Physik that year. It also calculated the specific heat and electrical resistance of metals.
The waves he described are now called Bloch waves or Bloch states, and the result is known as Bloch's theorem. Mathematicians had met similar equations before, notably in the work of Gaston Floquet, but Bloch was the one who saw their meaning for electrons in solids. Robert Hofstadter's memoir for the National Academy of Sciences says the importance of the paper can hardly be overstated, because it provided the basis for the band theory of condensed matter.
Others built quickly on it. A. H. Wilson used Bloch's bands to explain the difference between metals and insulators and to develop the theory of semiconductors. That understanding made it possible to replace fragile vacuum tubes with rugged semiconductor devices, the foundation of modern radio, television, computers and communications.
Why it matters
Bloch's theory of electrons in crystals underlies band theory and the physics of semiconductors, and therefore transistors, computer chips and modern electronics.
About Felix Bloch
Swiss-born physicist who laid the quantum foundations of solid-state physics, discovered nuclear magnetic resonance – the basis of MRI – and became CERN’s first director-general.
More about Felix Bloch
- Felix Bloch helped explain how particles slow in matterIn Copenhagen in the early 1930s, Felix Bloch refined Hans Bethe’s theory of how charged particles lose energy in matter, work remembered in the Bethe–Bloch formula.
- Felix Bloch's equations underpin MRIIn 1946 Felix Bloch wrote the Bloch equations for nuclear magnetisation, introducing the T1 and T2 relaxation times that later helped make MRI a powerful medical tool.
- Felix Bloch was CERN's first director-generalIn 1954 Felix Bloch became the first director-general of CERN, the new European laboratory for particle physics, as construction began on its site at Meyrin near Geneva.
- Felix Bloch measured the neutron's magnetismIn 1939, working with Luis Alvarez at the Berkeley cyclotron, Felix Bloch measured the neutron's magnetic moment to about one percent accuracy, a theorist turned experimenter.
- Felix Bloch's method became chemistry's key toolChemical shift experiments in Felix Bloch's own laboratory helped turn nuclear magnetic resonance into the most important spectroscopic tool in chemistry.
- Felix Bloch discovered how to listen to atomic nucleiIn 1946 Felix Bloch, William Hansen and Martin Packard at Stanford developed nuclear induction, one of the two founding methods of nuclear magnetic resonance.
- Felix Bloch described magnetic domain walls and spin wavesFelix Bloch described the boundaries between magnetic domains, now called Bloch walls, and proposed spin waves, partly in a paper written in hospital after a climbing accident.
Sources
- Felix Bloch Wikipedia
- Felix Bloch: Biographical NobelPrize.org
- Bloch's theorem Wikipedia
Another act of tikkun olam. This is part of tikkun olam, the Jewish idea of repairing the world, and every one of us can add to it.