Felix Bloch

Major contributions

• Developed Bloch's theorem (1929), showing that electron wavefunctions in a periodic crystal potential take the form of a plane wave modulated by a periodic function — the essential mathematical foundation of modern band theory and solid state electronic structure calculations
• Co-developed nuclear magnetic resonance (NMR) techniques (1946, independently of and simultaneously with Edward Purcell), providing a precise method for measuring nuclear magnetic moments that became foundational to both physics and, later, medical MRI imaging
• Made significant contributions to the theory of ferromagnetism and spin waves, and to superconductivity theory, across a broad and productive career in theoretical condensed matter physics
• Served as the first Director-General of CERN (1954–1955), helping establish the newly founded European laboratory during its critical early organisational period

Named concepts

Concept	Statement	Codex page
Bloch's Theorem	Electron wavefunctions in periodic potentials	View entry
Bloch Wall	Boundary region between magnetic domains	View entry

Career

Bloch studied under Werner Heisenberg at Leipzig, completing his doctorate in 1928 with a dissertation on the quantum mechanics of electrons in metals — work that directly led to his landmark 1929 theorem the following year. He emigrated to the United States in 1934, joining Stanford University, where he would spend the majority of his career (with a wartime interlude contributing to the Manhattan Project's early stages before shifting to radar-countermeasures research).

After the Second World War, Bloch turned his research attention to nuclear magnetic resonance, developing (simultaneously with, but independently of, Edward Purcell at Harvard) practical techniques for precisely measuring the magnetic properties of atomic nuclei using radio-frequency electromagnetic fields — work that earned both physicists a shared 1952 Nobel Prize in Physics, and that decades later became the essential physical basis for magnetic resonance imaging (MRI) in medicine.

Key publications

• Bloch, F. (1929). "Über die Quantenmechanik der Elektronen in Kristallgittern." Zeitschrift für Physik, 52(7–8), 555–600.

Nobel Prize

Felix Bloch shared the Nobel Prize in Physics for 1952 (with Edward Purcell) "for their development of new methods for nuclear magnetic precision measurements and discoveries in connection therewith" — notably, this prize recognised his later NMR work rather than his equally significant, earlier 1929 theorem on electrons in crystals.

Historical context

Bloch's career illustrates a pattern seen with several other physicists profiled in this Codex (compare, for instance, Kamerlingh Onnes): his Nobel Prize recognised a later achievement (NMR) rather than his earlier, arguably equally foundational contribution to physics (Bloch's theorem), which had by 1952 already become one of the standard tools of condensed matter theory without itself being separately honoured. Bloch's theorem remains, to this day, a required starting point in virtually every introductory course on solid state physics.