Interplay between High-Temperature Superconductivity, Magnetism and Composition in Doped Cuprates

Project Information

SUMAC

Grant agreement ID: 838926

DOI

10.3030/838926

Project terminated on 31 January 2023

EC signature date 10 April 2019

Start date 2 November 2020

End date 23 April 2023

Funded under

• EXCELLENT SCIENCE - Marie Skłodowska-Curie Actions

Total cost

€ 219 312,00

EU contribution

€ 219 312,00

Coordinated by

KOBENHAVNS UNIVERSITET
Denmark

Periodic Reporting for period 1 - SUMAC (Interplay between High-Temperature Superconductivity, Magnetism and Composition in Doped Cuprates)

Reporting period: 2020-11-02 to 2022-11-01

Summary of the context and overall objectives of the project

The Action "Interplay between High-Temperature Superconductivity, Magnetism and Composition in Doped Cuprates" (SUMAC for short) aims at unraveling the origin of high-temperature superconductivity - one of the greatest unsolved problems in physics. Superconductors are materials that can conduct electricity without any resistance and therefore without energy loss: superconductors could be seen as the most efficient means of energy transport. As a result, these materials exhibit great potential for many applications, for example in the energy, IT and transport sectors. While this could make a large impact for society, there is a major challenge to overcome: no superconductivity has been observed at room temperature, under normal atmospheric conditions, greatly limiting its potential. In fact, the origin of superconductivity is not yet fully understood. Cuprates are a particular class of superconductors, with their unique crystal structure, and these materials are the topic of this Action. It is well-known that the superconducting properties of cuprates are affected by their composition and doping. However, there is also ample evidence that the magnetic properties of cuprates are correlated to the superconducting properties, but a true understanding remains. Therefore, the main research question of SUMAC is: does the superconducting mechanism has its origin in the magnetic properties of the material? The objectives of SUMAC are to (1) synthesize cuprates (powders, pellets and crystals) with various chemical compositions and doping, and to (2) determine the superconducting and magnetic properties of the synthesized compounds. Neutron scattering plays an important role in this action, as it is the go-to technique to study both the static and dynamic magnetic properties of compounds, that are suspected to play a large role to the superconducting properties.

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

During the time of SUMAC, the researcher has successfully synthesized various cuprate compounds and worked on three subprojects that all deal with the question of how magnetism and superconductivity are related. A description of each subproject is given below:
1. Cuprates are only superconducting when they exhibit a particular number of free carriers, such as electrons or holes (which is the absence of an electron), and these carriers are introduced in the material by varying their composition. This process is called doping. By studying cuprate samples with slightly different doping, at the border of the critical amount of doping needed to obtain superconductivity, the researcher has investigated how superconductivity emerges when the amount of doping is increased. Notably, the researcher found that at this border of critical doping, the dynamic magnetism appears to be rather independent on the amount of doping, while the superconductivity is vastly different. The study of the gradual emergence of superconductivity led to a paper that is currently under peer review for publication.
2. Following the suggestion that superconductivity and magnetism are anticorrelated in the cuprate system, that is magnetism is suppressed when superconductivity is enhanced and vice versa, the researcher perturbed the magnetism in a cuprate compound by applying uniaxial stress. In this particular cuprate compound, it was previously shown that the superconducting properties where enhanced when uniaxial stress was applied to the crystal. The researcher used neutron scattering to directly probe the magnetism of the sample when uniaxial stress was applied. And indeed, it was found that applying stress does diminish the magnetism in the cuprate, responsible for the previously observed increase in superconductivity. This work let to a paper that is currently under peer review for publication, as well as a second manuscript that describes the custom-made pressure cell used in this study.
3. In addition to subproject 1, the researcher found that some low-energy magnetic correlations play a vital role at the critical doping levels. Some initial neutron scattering data revealed how the magnetism turns from a static form into a dynamic form, but further work is required to get the full picture. A follow-up neutron experiment is scheduled for early 2023.

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)

In addition to the three subprojects described above, the Action opened up a new avenue of research that the researcher continues to work on now that time of SUMAC officially came to an end. A particular type of cuprates in which electrons are the main carriers, requires a unique chemical treatment in order to show superconductivity: after synthesizing this compound, a post-treatment in which the sample is heated to 940 °C under a constant nitrogen flow is needed for the material to become superconducting. The researcher aims to investigate how this post-treatment affects the material’s magnetic properties and a neutron experiment is scheduled for early 2023.
Studying both sides of the phase diagram (the side where the free carriers are electrons and the side where the carriers are holes) will add significantly to the understanding of the superconducting mechanism and its relation to the magnetic properties of the material. This will bring us one step closer to the possibility of having room temperature superconductivity, which would be highly beneficial for the energy transition we are trying to achieve.

Schematic of superconductor resistivity and photos of cuprate samples