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The unique band structure of topological insulators gives rise to insulating bulk and unusual metallic surface properties. By tuning the content of Sb in the ternary compound (Bi_1–xSb_x)₂Te₃, Wang and collaborators show it is possible to control the precise features of the band structure in a continuous fashion.

The exact mechanism for superconductivity in iron-based superconductors remains elusive, but is thought to involve complex interactions between many orbitals. Using angle-resolved photoelectron spectroscopy, Liuet al. report the electronic structure of the single-layer parent compound FeSe.

The magnetic field dependence of the electrical resistance of topological insulators is not well understood. Zhang et al.now incorporate a magnetic topological insulator into a field effect transistor and identify unconventional magnetoresistance behaviour that could be useful in sensing and data storage.

The electron dephasing mechanism in topological insulators remains unclear. Here, Liaoet al. report a sublinear power law for the temperature dependence of the electron dephasing rate in (Bi,Sb)₂Te₃thin films, representing a surprising deviation from conventional behaviours in two-dimensional electron systems.

Potential Majorana bound states are seen in the vortex cores of a transition metal dichalcogenide. The properties of the superconductor mean that the bound states are highly anisotropic, and can appear at higher temperatures than other materials.

The coexistence of topological and superconducting states in a single layer of FeSe on a SrTiO₃ substrate is reported.

The authors study monolayer FeSe via scanning tunneling microscopy and simultaneous micron-scale-probe-based transport. They observe distinct superconducting phases in domains and on boundaries between domains, with different superconducting gaps and pairing temperatures.

The electric field generated by a gate electrode is exploited to trigger a reversible ferromagnetic–paramagnetic phase transition in a magnetic topological insulator close to a quantum critical point.

By growing a topological insulator on top of a high-temperature superconducting substrate it is possible to induce superconductivity in the surface states of the topological insulator. Moreover, the pairing symmetry of the induced superconductivity is s-wave, unlike the d-wave symmetry of the substrate.

The unconventional superconductivity associated with iron pnictide materials has been the subject of intense interest. Using an annealing procedure to control the charge-carrier concentration, the behaviour of an FeSe monolayer deposited on SrTiO₃ is now investigated, and indications of superconductivity at temperatures up to 65 K observed.

The discovery that potassium-doped iron selenide undergoes phase separation into a defect-free superconducting phase and an iron-vacancy-ordered insulating phase resolves many questions about the unusual behaviour of this iron-based superconductor.

There are many two-dimensional superconductors, but only now have monolayers of metallic atoms shown superconductivity. Grown on silicon substrates, epitaxial films of lead and indium represent the thinnest superconductors possible.

The critical temperature of single-layer FeSe films is much higher than the bulk of other iron-based superconductors, but the mechanism for this is unclear. Adding to the puzzle, Liu et al.show that it is much more difficult to induce superconductivity in a double-layer FeSe film than a single layer.

The origin of interface charge transfer and electron-phonon coupling in single unit-cell FeSe on SrTiO₃ remains elusive. Here, Zhang et al. report strengthened Ti-O bond and band bending at the FeSe/SrTiO₃ interface, which leads to several important processes.