Since its discovery, superconductivity has been a most intriguing phenomenon in solid-state physics. Although researchers in the early eighties thought that its mechanisms were already well understood, the discovery of unconventional superconductivity at high temperatures in copper- and iron-based materials flipped the tables, prompting a flurry of studies seeking to explain the underlying mechanisms.

In particular, iron selenide exhibits several unique physical properties, many of which have only been explored theoretically and are yet to be observed. Now, in an effort to keep other scientists up to date, experimental physicists from Japan have condensed over a decade of research in this field into a review article.

In the article, they go over the exotic superconducting properties of iron selenide, such as anisotropic superconductivity, magnetic-field induced superconducting states, BCS-BEC crossover, electronic nematicity, and topological superconductivity, as well as experimental methods to explore the origin of superconductivity, which could be a peculiar type of electron pairing.

One approach employed by the authors themselves is using scanning tunneling microscopy to observe standing waves of electrons on the surface of iron selenide superconductors at different tunneling energies. This provides insight into the electronic structure of the material and its superconducting energy gap, which is fundamental to understanding the superconducting state.

The authors believe that iron selenide superconductors will be key to understanding unconventional superconductivity so that someday, a superconductor that operates at room temperature and atmospheric pressure can be developed. Such a feat would revolutionize the energy and electronics fields. Moreover, superconductivity may play a fundamental role in quantum computers. This review article will hopefully make research progress in superconductive iron selenides more accessible, thereby inspiring experimental research.