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(Towards) Room Temperature Superconductivity
The search for a room-temperature superconductor, which would have an enormous potential for practical applications, has been one of the biggest challenges in solid state physics in the last one hundred years. For many of the known superconductors there is little consensus on fundamental issues such as the very nature of the pairing mechanism, the relation/competition with other ordering phenomena (spin and charge order, nematic fluctuations), the effect of strong electronic correlations. This strongly limits the predictive power of superconducting theories. On the other hand, a decade of experience has shown that in the simple case of electron-phonon mediated superconductivity, where the details of the microscopic pairing are understood, first-principles calculations can be used to quantitatively describe materials. Combined with recent high-throughput screening methods, this can lead to the prediction of new compounds. To achieve the same level of description in the unconventional materials requires a better understanding of the existing theoretical models, in order to extend their applicability to ab-initio electronic structure methods. The present challenge in the field is therefore to formulate a predictive, parameter-free, theory of superconductivity of general applicability to any class of superconductors.
The aim of our workshop was to bring together a selection of top researchers in the field of superconductivity and high-throughput methods to bridge the two communities and formulate strategies for an intelligent search of new and better superconductors. One of the most discussed topics was how to distill the present empirical knowledge in the field into a set of “descriptors”, i.e. quantities which easy to calculate from first principles, and correlate with desirable superconducting properties. These can be exploited in conjunction with high-throughput techniques, which employ methods from artificial intelligence to screen large sets of material data. Another widely-discussed topic was how to optimize existing materials, using new experimental techniques which permit to control structure and doping much more efficiently than traditional chemistry methods. In particular, polymer gating, interfacing and heterostructures were discussed. Empirical observation has also shown that superconductivity often occurs close to an instability in the phase diagram: this suggests that good “fishing spots” for superconductors are materials with incipient structural instabilities or fragile magnetism. It was also observed that one of the main challenges is currently to find a way to quantitative describe spin fluctuations, and in this sense the interaction between ab-initio and model theorists was very fruitful.
During the five days of the workshop, we have tried to create an informal atmosphere and to promote interaction between the participants, encouraging open discussions during the talks and flexible schedules. This was particularly appreciated, because it led to a fruitful exchange of ideas between researchers who work in traditionally separate fields. The healthy balance between experienced and younger researchers was also very important to ensure that the rich and detailed understanding acquired in the field in the last fifty years (many-body theory and modeling, “traditional” density functional theory) can be combined with the latest computational and technological achievements (high-throughput methods, polymer gating, heterostructures, beyond-DFT methods).
We can surely say that the meeting was a great success, as the feedback of all participants was very positive, and many ideas for collaborations have emerged during the workshop. This would never have been possible without the support of the Lorentz Center and Cecam which we gratefully acknowledge.
Lilia Boeri (Graz, Austria)
Eberhard Gross (Halle, Germany)
Antonio Sanna (Halle, Germany)