The Ginzburg–Landau theory, which combined Landau's theory of second-order phase transitions with a Schrödinger -like wave equation, had great success in explaining the macroscopic properties of superconductors. In particular, Alexei Abrikosov showed that Ginzburg–Landau theory predicts the division of superconductors into the two categories now referred to as Type I and Type II. Abrikosov and Ginzburg were awarded the 2003 Nobel Prize in Physics for their work (Landau having died in 1968). Also in 1950, Emanuel Maxwell and, almost simultaneously, C.A. Reynolds et al. found that the critical temperature of a superconductor depends on the isotopic mass of the constituent element. This important discovery pointed to the electron-phonon interaction as the microscopic mechanism responsible for superconductivity.