In 1936 he discovered
paramagnetic relaxation; however, he missed the discovery of
nuclear magnetic resonance (otherwise known as nuclear spin resonance), as described by
Joan Henri Van der Waals. With
Hendrik Casimir he devised a two-fluid model to explain
superconductivity with
thermodynamics and
Maxwell's equations. Casimir described their collaboration in one of his books. The "Gorter-model" for a second-order phase transition is from this period of his career, as well as the elucidation of the
Senftleben effect (change of
viscosity and thermal conductivity of paramagnetic gas in a magnetic field). The second-order phase transition was for a while controversial, as it seems to require two sheets of the Gibbs free energy to osculate exactly, which is so unlikely as to never occur in practice. Gorter replied the criticism by pointing out that the Gibbs free energy surface might have two sheets on one side, but only one sheet on the other side, creating a forked appearance. ( pp. 146--150) Gorter studied many aspects of
antiferromagnetism in
CuCl2·2H2O. With Johannes Haantjes, he developed a theoretical model of antiferromagnetism in a double-lattice substance. After WWII he worked on liquid
helium II and developed the theory which is now known as
Coulomb blockade, the increase in electrical resistance in metal films at low temperatures. The Gorter-Mellink equation describes the mutual friction of two fluids in liquid helium II. ==Prizes and honors==