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Common Threads in the Electronic Phase Diagram of Unconventional Superconductors
Scientific Report: Common threads in the Electronic Phase Diagram of Unconventional Superconductors
M. Allan, T. Das, N. Hussey, C. Panagopoulos, J. Zaanen
Last few years have been exceptionally prolific for superconductivity, with the discoveries of several new materials classes, inventive heterostructures, novel tuning parameters, new intertwined phases, and strange metals with or without a critical point at the superconducting dome. These discoveries have led to new insights which have revived some of the earlier understandings. A basic theme of the workshop was to explore and unify the common properties, combining both earlier and recent results, displayed in all classes of unconventional superconductors including copper-oxides, heavy-fermions, organics, newly discovered iron-pnictide, chalcogenides, and various heterostructures.
In our workshop, we aimed to bring some order in the new landscape though teaching each other about our “niches”, and by then discussing in groups and in the plenary about the big picture. We concentrated on the common threads that emerge in all families of new superconductors.
We started by exploring new experimental methods and tunabilities which can enable to individually control the correlated physics and superconductivity with the goal to illuminate how their interplay results in strong Cooper pairing. Experts from all fields discusses on designing focused experiments which can be carried out in all materials families so that common and important features can be unraveled. Substantial emphasis was given to utilize the recently developed high-resolution spectroscopies, and multifaceted sample preparation techniques, and multiple tunings methods. An equal focus was given to the theoretical aspects of both electronic correlation and superconductivity where existing approaches based on strong coupling or weak coupling theories are challenged. A question of general interests is why and how superconductivity often emerges near the boundary between the strong coupling, local and weak coupling, Fermi-liquid like regimes with the cooperation of enhanced non-Fermi liquid physics. We have discussed several newly developed theories for the non-Fermi liquid or strange metal physics without tuning the materials to a quantum critical point. Intermediate coupling (where electronic interaction strength is of the order of bandwidth) models for correlated superconductors, recently observed charge density wave, pair density wave, nematic order for superconductivity, and others will be discussed and confronted with experiments. Given the diversity and versatility of the field, focused and well-defined problems are identified where collaborations between experiment and theory can be build and strengthened.
The workshop was a success in terms of achieving these goals. In particular, we have discussed in depth that the Non-Fermi liquid behavior is a generic and common parameter which precedes superconductivity in all families of superconductors. This conclusion was achieved after sifting through gamut of experimental data and discussions. It was appreciated by all participants and took it as a focus research topic in the future. We had break-out discussions which were enjoyable and fruitful. All talks were also distributed as 30 minutes talks and 15 minutes discussion. The talks were also informal with lots of discussion throughout the talks. All participants were very happy the format of the program, and enjoyed experimenting with new ways of discussing.
It was a very nice and fruitful week, and we are very grateful for the tremendous enthusiasm the participants brought to the workshop!