A silver path to a new generation of quantum materials.

Project Information

SILVERPATH

Grant agreement ID: 893943

DOI

10.3030/893943

Project closed

EC signature date 19 March 2020

Start date 1 October 2020

End date 30 September 2022

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 171 473,28

EU contribution

€ 171 473,28

Coordinated by

CONSIGLIO NAZIONALE DELLE RICERCHE
Italy

Periodic Reporting for period 1 - SILVERPATH (A silver path to a new generation of quantum materials.)

Reporting period: 2020-10-01 to 2022-09-30

Summary of the context and overall objectives of the project

Silver(II) fluoride is a strongly correlated insulator, with characteristics remarkably similar to those of parent high-temperature superconducting cuprates but also significant differences. To quantify the degree of similarity between the two families of materials in terms of parameters has been one of the aims of the project. The similarities with cuprates suggest that AgF2 has the potential to be the basic building block to a new class of strongly correlated materials with similar properties. Since high temperature superconductors have a large field of applications, it is possible that superconductors based on silver fluorides can also find a niche. Furthermore, finding a new superconductor with similar characteristics as those of cuprates can help solve several remaining mysteries of their mechanism.

The purpose of SILVERPATH was to develop appropriate models to characterize and predict magnetic, metallic and superconducting properties of silver fluorides and related materials by combining analytical and computational methods. In doing so, we have fostered a strong collaboration with the chemist group of W. Grochala (Warsaw). This has strengthened the transfer of knowledge between condensed matter physics and chemistry communities.

We have significantly advanced in understanding the electronic properties of bulk AgF2 by developing appropriate models and realistic parameters. The strength of correlations in bulk AgF2 has been thoroughly studied, which allows us to classify the material as a charge-transfer correlated insulator, confirming the material is a cuprate analogue. A route for charge doping flat monolayer AgF2 in a chemical capacitor setup has been found and studied, working in close collaboration with the chemistry group at Warsaw. The electron doping path has been found particularly promising in terms of control of doping and superconductivity.

A very promising new route to superconductivity has also been explored in related quantum materials, where the interaction is mediated by the coupling to polar fluctuations instead of spin fluctuations. An example of possibly relevant materials are SrTiO3, KTaO3 and related oxide heterostructures. We have also significantly advanced in understanding the coupling to polar fluctuations in these systems by developing appropriate models and realistic parameters. These materials are very interesting because they have both a ferroelectric and a superconducting phase, which may lead to interesting possibilities to control superconductivity and potential applications in devices.

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

The strength of correlations in bulk AgF2 has been thoroughly studied, which is a crucial step for establishing appropriate models and parameters and classifying AgF2. Combining band photoemission and Auger-Meitner spectroscopy of AgF and AgF2 together with computations in small clusters, values of the Coulomb interaction and charge-transfer energy have been estimated. This work has been published in Physical Review B (2022).

We have explored the optimal charge doping to flat AgF2 monolayers for superconductivity, and explored different chemical ways of doping it, in close collaboration with the Chemistry group in Warsaw. This work has been published in Phys. Chem. Chem. Phys. (2022) and was selected by the editors as a “2022 HOT PCCP article”.

In the last few years a related class of quantum materials has surfaced, polar systems, with experimental indication that the proximity of the polar phase could play a role in mediating superconductivity. We have studied a novel pairing mechanism in these polar systems, where a Rashba-like interaction to the polar modes is assisted by spin-orbit coupling. The pairing strength in the incipient polar material SrTiO3 has been estimated and found it can support bulk superconductivity. This work has been published in Phys. Rev. B (2022) and a second manuscript with an in-depth characterization of the coupling is under review in Phys. Rev. Research. The same Rashba-like interaction has recently shown promise for superconductivity in bulk KTaO3 and related heterostructures. We have extended our formalism to this material and shown it has some intrinsic anisotropic properties and a promisingly large pairing strength. A manuscript of this work is under review in JPhys Materials IOP journal for the Focus Issue on "Women's Perspectives in Quantum Materials".

The main results have been presented in several international conferences.

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)

Combining computations and experiments done at Warsaw we have been able to determine microscopic parameters of AgF2 which were not known. This sets the ground for future theoretical computations of the electronic structure of these materials. Furthermore, we have devised ways of controlling the charge of AgF2 layers, which will guide ongoing experimental efforts to produce high temperature superconductors with these materials. Previous works have predicted that the superconducting critical temperature can surpass cuprates. If this is verified, a large benefit will result for society. For example, many decarbonisation applications use high-temperature superconductors (superconducting motors and generators, magnets for nuclear fusion reactors, fault current limiters). Thus, a superconductor with a higher critical temperature than present day materials may help the widespread use of these technologies with a large impact in realizing a carbon-neutral society.

A layer of AgF2 (OX) was studied with different partner layers to achieve d-wave superconductivity.