Vitaly Lazarevich Ginzburg (pictured) has died, aged 93. In life, he was celebrated for his numerous achievements to several areas of physics. Moreover, like many towering scientists of a bygone age, he was an active citizen who made lasting contributions to life in his country, well beyond the realm of physics or even science. In the 1990s, during the declassification of Soviet intelligence files, we learned of his part in the development of the hydrogen bomb for the Soviet Union. Ginzburg himself said that this activity probably saved him from the firing squad (or at least from unemployment) around the time of the 'doctor's plot', a period in which a “totally insane” Stalin accused a number of doctors, more than half of whom were Jewish, of plotting to kill top government officials.

Credit: © RIA NOVOSTI/SCIENCE PHOTO LIBRARY

Despite his fame in plasma physics and astrophysics, not to mention nuclear physics, his greatest legacy is the Ginzburg–Landau theory of superconductivity. The Ψ-theory, as he called it, predates the microscopic Bardeen–Cooper–Schrieffer (BCS) theory of superconductivity and is a triumph of physical intuition and ingenuity. Incidentally, having been born in 1916, Ginzburg had a rather unconventional education owing to the First World War and its aftermath, only managing four years of formal schooling before gaining entrance to Moscow State University by open examination. Perhaps his unorthodox path is the reason why his approach to superconductivity is so intuitive and practical — a true workhorse theory for students not necessarily versed in second quantization and other advanced theoretical gymnastics required for BCS.

But back to Ginzburg–Landau theory. It is essentially based on Lev Davidovich Landau's theory of type-II phase transitions applied to a charged fluid; technically, it introduces a gradient term that couples to the vector potential and allows for a complex wavefunction. Without any knowledge of the microscopic structure (that is, the existence of paired electrons), it is possible to write down the free energy of the system. When minimized, two equations emerge. The first looks like a Schrödinger equation plus a nonlinear term, heralding some kind of macroscopic wavefunction Ψ, or coherent behaviour. The second equation is identical to the quantum mechanical definition of current. These two expressions, together with Maxwell's equation for magnetic field, lead to the following: (i) the magnetic screening (Meissner effect) and critical magnetic field above which the superconductor is no longer superconducting; (ii) the extent to which the magnetic field can penetrate the surface (penetration depth λ); (iii) the first London equation (which leads to the supercurrent, or electrical flow without resistance); (iv) the coherence length (ξ) of the wavefunction; (v) flux quantization; and (vi) the vortex lattice, in which the vortices through which magnetic flux can penetrate the superconductor are arranged geometrically. In a nutshell, this descriptive theory yields all the properties of a superconductor, except for the transition temperature and superconducting gap structure. And remarkably, it works as well for conventional superconductors as it does for high-temperature superconductors.

His recognition by the Nobel foundation came late in life, when he was 87, but Ginzburg's achievements have been appreciated by working physicists for decades, and will continue to be for the foreseeable future.