Proc. R. Soc. Lond. A 371, 24-27(1980) Printed in Great Britain Memories of electrons in crystals BY F. BLOCH Department of Physics, Stanford University California, U.S.A Bloch. felix. Born Zurich, switzerland, 1905. Naturalized U. s. citizen. studied at Leipzig(Ph. D. 1928). Positions held: Utrecht(1930); Copenhagen(1931) Leipzig(1932); Rome(1933); Stanford (1934-42); Manhattan Project (1942-3) Radio Research Laboratory, Harvard University(1943-5); Professor, Stanford University(1945 to date). Fundamental contributions to electron theory of metals quantum theory of ferromagnetism, superconductivity. Nobel prize for phya Sics As a student in Zurich, it was my good forti t at the colle In which Schrodinger told the first time about his wave mechanics. When both he and Debye accepted positions in Germany I decided upon the latter's advice to continue my studies under Heisenberg in Leipzig, where I arrived in the autumn of 1927 Already in Zurich my interests had turned from experimental to theoretical physics, and particularly towards quantum mechanics, and before coming te Leipzig I had started some calculations on the radiation-damping of wave-packets As the first thing, Heisenberg encouraged me to complete this work, later published in the Physikalische Zeitschrift, whereupon he considered me ready to start on a opic for my Ph. D, thesis Although his famous preceding work had not dealt with problems of state, Heisenberg felt by then-it was the beginning of 1928-that quantum mechanics could be fruitfully applied to this field of research. Referring to his earlier paper on the ortho-and para-states of the helium atom, he casually remarked to me that ferromagnetism had to be explained by a changed sign of the exchange energy between electrons so as to energetically favour parallel orientation of their spins. I realized that Heisenberg saw already the crux of the matter and I felt that there would be nothing essentially new left for me to contribute. Indeed, he shortly afterwards wrote the paper that laid the groundwork for the modern theory of ferromagnetism. It was not until two years later that I somewhat embellished his treatment by the introduction of spin waves which, subsequently, led me to the recognition of domain walls There was more of a challenge in another suggestion of his: to look into the theory of metals. During my earlier studies I had read the classical book of H. A. lorentz on the theory of electrons and it was obvious that his work, based on Boltzmann statistics, had to be modified. Pauli had already shown that the application of Fermi statistics led to the temperature-independent paramagnetism of conduction electrons, but the most important applications were made by Sommerfeld. He hadProc. R. Soc. Lond. A 371, 24-27 (1980) Printed in Great Britain Memories of electrons in crystals By F. BLOCH Department of Physics, Stanford University, California, U.S.A. Bloch, Felix. Born Zurich, Switzerland, 1905. Naturalized U.s. citizen. Studied at Leipzig (Ph.D. 1928). Positions held: Utrecht (1930); Copenhagen (1931); Leipzig (1932); Rome (1933); Stanford (1934-42); Manhattan Project (1942-3); Radio Research Laboratory, Harvard University (1943-5); Professor, Stanford University (1945 to date). Fundamental contributions to electron theory of metals, quantum theory of ferromagnetism, superconductivity. Nobel prize jor physics 1952. As a student in Zurich, it was my good fortune to be present at the colloquium in which Schrodinger told the first time about his wave mechanics. When both he and Debye accepted positions in Germany I decided upon the latter's advice to continue my studies under Heisenberg in Leipzig, where I arrived in the autumn of 1927. Already in Zurich my interests had turned from experimental to theoretical physics, and particularly towards quantum mechanics, and before coming to Leipzig I had started some calculations on the radiation-damping of wave-packets. As the first thing, Heisenberg encouraged me to complete this work, later published in the Physikalische Zeitschrift, whereupon he considered me ready to start on a topic for my Ph.D. thesis. Although his famous preceding work had not dealt with problems of the solid state, Heisenberg felt by then - it was the beginning of 1928 - that quantum mechanics could be fruitfully applied to this field of research. Referring to his earlier paper on the ortho- and para-states of the helium atom, he casually remarked to me that ferromagnetism had to be explained by a changed sign of the exchange energy between electrons so as to energetically favour parallel orientation of their spins. I realized that Heisenberg saw already the crux of the matter and I felt that there would be nothing essentially new left for me to contribute. Indeed, he shortly afterwards wrote the paper that laid the groundwork for the modern theory of ferromagnetism. It was not until two years later that I somewhat embellished his treatment by the introduction of spin waves which, subsequently, led me to the recognition of domain walls. There was more of a challenge in another suggestion of his: to look into the theory of metals. During my earlier studies I had read the classical book of H. A. Lorentz on the theory of electrons and it was obvious that his work, based on Boltzmann statistics, had to be modified. Pauli had already shown that the application of Fermi statistics led to the temperature-independent paramagnetism of conduction electrons, but the most important applications were made by Sommerfeld. He had [24]