The interrelation of electronic order with antiferromagnetism and superconductivity has recently emerged as a vital question for rationalizing the physics of all classes of unconventional superconductors. Typically, such electronic ordering phases, which recently have been dubbed intertwined phases, are ubiquitously found at the crossover between ostensibly competing antiferromagnetic and superconducting states. Only rarely the electronic order is sufficiently long-range correlated to render it susceptible for diffraction techniques. Instead, it usually requires a local probe to detect it experimentally. It is clear, however, that such a probe must provide sensitivity at the same time to electronic order, superconductivity, and static magnetism for a full characterization of the intertwined phases, aiming at clarifying the interrelation between these ordering phenomena. The only experimental technique which is capable of fulfilling these requirements simultaneously is spin-polarized scanning tunnelling microscopy (SP-STM), which to the best of our knowledge, has never been applied to this intriguing problem, despite the apparent mandatory necessity.
For this purpose, a unique milli-Kelvin scanning tunnelling microscope (STM) is being built, which will make possible to access the ground states of all these systems, and to achieve maximum resolution in energy and real-space. This new instrument aims at studying the most important classes of unconventional superconductors, viz. cuprate, iron-arsenide, and heavy-fermion superconductors.
Further experimental and theoretical work within this project aims to better rationalize the physics of unconventional superconductors and correlated phases. For example, we address nematicity in iron-based superconductors as well as strongly underdoped correlated phases close to the Mott transition, including the mechanism of the doping-induced insulator-metals transition. Thus we hope contributed to the still sought-after complete rationalization of this physics which indeed is the crucial milestone required to eventually achieve superconductivity at technologically better exploitable temperatures. This, eventually, can be expected to open up new technologies ranging from energy saving to quantum computing.
