New type of magnetism unveiled in an iconic material


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Since the discovery of superconductivity in the Sr2RuO4 in 1994, hundreds of studies were published on this compound, which suggested that Sr2RuO4 is a very special system with unique properties. These properties make Sr2RuO4 a material with high potential, for example, for the development of future technologies including superconducting spintronics and quantum electronics thanks to its ability to simultaneously convey lossless electric currents and magnetic information. An international research team led by scientists from the University of Constance has now been able to answer one of the most interesting open questions about Sr2RuO4: Why does the superconducting state of this material exhibit certain characteristics that are commonly found in materials known as ferromagnetics, which are considered to be antagonists of superconductors? The team discovered that Sr2RuO4 harbors a new form of magnetism, which can coexist with superconductivity and also exists independently of superconductivity. The results were published in the latest issue of Natural communications.

After a research study that spanned several years and involved 26 researchers from nine different universities and research institutes, the missing piece of the puzzle appears to have been found. Alongside the University of Constance, the universities of Salerno, Cambridge, Seoul, Kyoto and Bar Ilan as well as the Japan Atomic Energy Agency, the Paul Scherrer Institute and the Centro Nazionale delle Ricerche participated in the study.

So far not the right tool for finding evidence

“Despite decades of research on Sr2RuO4, there had been no evidence of the existence of this unusual type of magnetism in this material. A few years ago, however, we wondered whether the reconstruction that occurs in this material on the surface, where the crystal structure shows some small changes at the atomic scale, could also lead to electronic order with magnetic properties. Following this intuition, we realized that this question had probably not been addressed because no one had used the “right tool” to find evidence of this magnetism, which we thought could be extremely weak and limited to a few. atomic layers of the surface of the material “says the head of this international research study, Professor Angelo Di Bernardo of the University of Constance, whose research focuses on spintronic and quantum superconducting devices based on innovative materials.

To perform the experiment, the team used high quality single crystals from Sr2RuO4 prepared by the group of Dr Antonio Vecchione of the Centro Nazionale delle Ricerche (CNR) Spin in Salerno. “Make large crystals of Sr2RuO4 without any impurities was a great challenge although crucial for the success of the experiment, as the defects would have given a signal similar to the magnetic signal we were looking for, ”explains Dr Vecchione.

The right tool is a muon beam

The special “tool” the researchers used to unveil the new magnetism is a beam of particles called muons that are produced in a particle accelerator in Switzerland at the Paul Scherrer Institute (PSI). “At PSI, we have the only facility in the world to produce implantable muons with an accuracy of a few nanometers. These particles, which can be used to detect extremely tiny magnetic fields, could be arrested very close to Sr.’s surface.2RuO4, which was crucial for the success of the experiment, ”says Dr. Zaher Salman, who coordinated the experiment at the PSI muon facility.

“It has been a very nice experience taking measurements at an international beam facility like PSI and interacting with such a large group of inspiring scientists from all over the world, since the very beginning of my PhD in Constance,” says Roman. Hartmann, doctoral researcher who also contributed as the first author to the study.

The authors also developed a theoretical model suggesting the origin of this hidden surface magnetism. “Unlike conventional magnetic materials whose magnetic properties derive from the quantum mechanical property of an electron known as spin, a cooperative swirling motion of interacting electrons, generating circulating currents at the nanoscale, sub- tends the magnetism discovered in Sr2RuO4“says Dr Mario Cuoco of CNR-spin who developed the theoretical model with Dr Maria Teresa Mercaldo and other colleagues from the University of Salerno.

New perspectives for basic and applied research

As Professor Jason Robison of the University of Cambridge has pointed out, the results confirm that “the physical properties can be significantly altered at the surface of a complex material and at the interfaces within thin-film heterostructures, and these modifications can be exploited to discover new and applied research, including the design and development of quantum devices.

The co-authors of the project also include Professor Yoshiteru Maeno of Kyoto University, the scientist who first discovered superconductivity in Sr2RuO4 in 1994 and which contributed to some of the most important studies of this material reported in the last 30 years.

“This discovery not only solves a long-standing puzzle and makes the iconic material Sr2RuO4 even more interesting than before, but may also trigger new research that will eventually help answer other striking open questions in materials science, “says Professor Elke Scheer of the University of Constance, another of the project leaders and leader of the mesoscopic systems research team.

The new type of magnetism discovered in Sr2RuO4 is essential to better understand the other physical properties of Sr2RuO4 including its unconventional superconductivity. The fundamental discovery may also lead to the search for this new form of magnetism in other materials similar to Sr2RuO4 as well as triggering new studies to better understand how such magnetism can be manipulated and controlled for new applications in quantum electronics.

Spontaneous superconducting currents in strontium ruthenate

More information:
R. Fittipaldi et al, Unveiling unconventional magnetism on the surface of Sr2RuO4, Nature Communication (2021). DOI: 10.1038 / s41467-021-26020-5

Provided by the University of Constance

Quote: New Kind of Magnetism Unveiled in Iconic Material (2021, October 5) retrieved November 6, 2021 from

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