Fritz London - Academic Achievements

Academic Achievements

London's early work with Walter Heitler on chemical bonding is now treated in any textbook on physical chemistry. This paper was the first to properly explain the bonding in a homonuclear molecule as H₂. It is no coincidence that the Heitler-London work appeared shortly after the introduction of quantum mechanics by Heisenberg and Schrödinger, because quantum mechanics was crucial in their explanation of the covalent bond. Another necessary ingredient was the realization that electrons are indistinguishable, as expressed in the Pauli principle.

Other early work of London was in the area of intermolecular forces. He coined the expression "dispersion effect" for the attraction between two rare gas atoms at large (say about 1 nanometer) distance from each other. Nowadays this attraction is often referred to as "London force". In 1930 he gave (together with R. Eisenschitz) a unified treatment of the interaction between two noble gas atoms that attract each other at large distance, but at short distance are repellent. Eisenschitz and London showed that this repulsion is a consequence of enforcing the electronic wavefunction to be antisymmetric under electron permutations. This antisymmetry is required by the Pauli principle and the fact that electrons are fermions.

For atoms and nonpolar molecules, the London dispersion force is the only intermolecular force, and is responsible for their existence in liquid and solid states. For polar molecules, this force is one part of the van der Waals force, along with forces between the permanent molecular dipole moments.

London was the first theoretical physicist to make the fundamental, and at the time controversial, suggestion that superfluidity is intrinsically related to the Einstein condensation of bosons, a phenomenon now known as Bose–Einstein condensation (BEC). Bose recognized that the statistics of massless photons could also be applied to massive particles; he did not contribute to the theory of the condensation of bosons.

London was also one of the early authors (including Schrödinger) to have properly understood the principle of local gauge invariance (Weyl) in the context of the then new quantum mechanics.

London predicted the effect of flux quantization in superconductors and with his brother Heinz postulated that the electrodynamics of superconductors is described by a massive field. I.e. that magnetic field decays exponentially in a superconductor with the exponent which is called now London length.

London also developed a theory of a rotational response of a superconductor, pointing out that rotation of a superconductor generates magnetic field London moment. This effect is used in models of rotational dynamics of neutron stars.