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MARS Report Summary

Project ID: 647276
Funded under: H2020-EU.1.1.

Periodic Reporting for period 1 - MARS (Electronic Order, Magnetism, and Unconventional Superconductivity probed in Real-Space)

Reporting period: 2015-09-01 to 2017-02-28

Summary of the context and overall objectives of the project

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.

The MARS project builds on our experience in the field of unconventional superconductivity and scanning tunnelling microscopy. Recently, we were able to establish SP-STM in our microscopes, and thus the time has now come to apply this technique for the first time on unconventional superconductors.
Exactly this is the goal of this project. Highest-resolution SP-STM will be systematically applied to prototype representatives of the most important classes of unconventional superconductors, viz. cuprate, iron-arsenide, and heavy-fermion superconductors. For this purpose, a unique milli-Kelvin scanning tunnelling microscope (STM) will be built which will make possible to access the ground states of all these systems with SP-STM, and to achieve maximum resolution in energy and real-space.

It can be expected, that a successful outcome of the project will lead to a better rationalization of the physics of unconventional superconductors. The complete rationalization of this physics indeed is the crucial milestone required to eventually achieve superconductivity at technologically better exploitable temperatures, which can be expected to open up new technologies ranging from energy saving to quantum computing.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

In the period covered, we have worked on constructing a new type of lowest-temperature scanning tunneling microscope (STM) which operates at 30mK. More specifically, the CAD model is ready, and all the commercial parts have been ordered. The assembly of the system is currently going on, on schedule. Furthemrore, the superconducting state and impurity states of LiFeAs have been investigated, the results have been published.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

Our work on the iron-pnictides revealed a very unconventional change of the superconducting state in LiFeAs. This finding underpins the special role of this material among the iron pnictides. Furthermore, the detailed study of impurity states and their impact on superconductivity has been performed which brings the scientific community closer to the aim to rationalize the physics of the iron pnictides.
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