€2.7 million for superconducting 'miracle'

TECHNISCHE UNIVERSITÄT DRESDEN

cerium-rhodium-arsenic (CeRh2As2) — IMAGE:
DEPICTED IS THE SUPERCONDUCTING MIRACLE CERIUM-RHODIUM-ARSENIC (CERH2AS2). THANKS TO A €2.7 MILLION GRANT FROM THE EUROPEAN RESEARCH COUNCIL, ELENA HASSINGER WILL BE ABLE TO ADVANCE HER RESEARCH ON THIS MATERIAL AT THE CLUSTER OF EXCELLENCE CT.QMAT FOR THE NEXT FIVE YEARS.
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CREDIT: JÖRG BANDMANN/CT.QMAT

Unconventional Superconductor CeRh2As2: A Quantum Superstar

The research conducted by Elena Hassinger, an expert in low-temperature physics working at ct.qmat—Complexity and Topology in Quantum Matter (a joint initiative by two universities in Würzburg and Dresden), has always been synonymous with extreme cold. In 2021, she discovered the unconventional superconductor cerium-rhodium-arsenic CeRh2As2). Superconductors normally have just one phase of resistance-free electron transport, which occurs below a certain critical temperature. However, as reported in the academic journal Science, CeRh2As2 is so far the only quantum material to boast two certain superconducting states.

Lossless current conduction in superconductors has remained a central focus in solid-state physics for decades and has emerged as a significant prospect for the future of power engineering. The discovery of a second superconducting phase in CeRh2As2, which results from an asymmetric crystal structure around the cerium atom (the rest of the crystal structure is completely symmetrical), positions this compound as a prime candidate for use in topological quantum computing. Hassinger plans to extend her search to other quantum materials with similar unusual structural properties, hoping to achieve topological superconductivity at higher temperatures.

ERC Consolidator Grant: €2.7 Million Boost from the European Research Council

The European Research Council has awarded Hassinger €2.7 million for her project “Exotic Quantum States by Locally Broken Inversion Symmetry in Extreme Conditions—Ixtreme.” Over the next five years, she intends to use this funding to further her study of the superconducting “miracle” CeRh2As2 in her Dresden laboratories, uncover related quantum materials, and contribute to a significant breakthrough in topological quantum computing. “If we can confirm the theoretical predictions of topological surface states on my cerium-rhodium-arsenic compound in the laboratory, this could pave the way for the creation of topological quantum bits (qubits). This would be a huge step forward,” Hassinger explains.

Huge Potential for Topological Quantum Computing

Topological qubits are known for their robustness, offering quantum states that are significantly more stable compared to their non-topological counterparts. One of the biggest challenges in current research is developing a method to sustain 1,000 qubits simultaneously. Achieving this would enable quantum processors to complete tasks in a matter of minutes that would take conventional supercomputers years. This is why the brilliant minds at ct.qmat are concentrating on research into topological quantum materials.

Groundbreaking Research under Extreme Laboratory Conditions

In her quest to investigate the unconventional superconductor cerium-rhodium-arsenic, Hassinger first needs a cryostat to cool the material sample to below 0.35 Kelvin (–272.8 degrees Celsius). “This machine costs over a million euros. Negotiations are already underway,” she reveals. When the sample is cold enough, it will be subjected to intense pressure and an ultra-strong magnetic field of up to 18 Tesla, vastly exceeding the 0.1 Tesla field of a typical horseshoe magnet. “Conducting these high-pressure magnetic field measurements could take several months, requiring precise daily adjustments,” Hassinger explains, outlining her experimental approach. Her goal is to closely examine the second superconducting phase of cerium-rhodium-arsenic in order to finally prove that the material is a topological superconductor. If successful, this “miracle material” would not only enable lossless electron conduction but also possess robust topological surface states that could potentially be used in quantum computing operations.

Outlook

“The European Research Council funds promising pioneering research with the ERC Consolidator Grant. Elena Hassinger is an experienced physicist who has discovered an exceptional material. With this new grant, she aims to be the first to experimentally characterize its exotic quantum states and also find related quantum states in similar materials at higher temperatures,” says Professor Matthias Vojta, ct.qmat’s Dresden spokesperson. “We’re thrilled to have her as part of our ct.qmat research family,” he adds.

About Elena Hassinger

Since the fall of 2022, Elena Hassinger has held ct.qmat’s Chair of Low-Temperature Physics of Complex Electron Systems, which is based at TU Dresden. She is also closely associated with the Max Planck Institute for Chemical Physics of Solids (MPI CPfS) in Dresden as a Max Planck Fellow. Notable achievements in her career include heading the independent research group Physics of Unconventional Metals and Superconductors at MPI CPfS since 2014 and a tenure-track professorship at TU Munich from 2016 to 2022.

Cluster of Excellence ct.qmat

The Cluster of Excellence ct.qmat—Complexity and Topology in Quantum Matter has been jointly run by Julius-Maximilians-Universität Würzburg and Technische Universität Dresden since 2019. Over 300 scientists from more than thirty countries and four continents study topological quantum materials that reveal surprising phenomena under extreme conditions such as ultra-low temperatures, high pressure, or strong magnetic fields. ct.qmat is funded through the German Excellence Strategy of the Federal and State Governments and is the only Cluster of Excellence in Germany to be based in two different federal states.

Links & Downloads
YouTube video (English language, German subtitles): „Transporting electricity without loss | #Introducing Elena Hassinger“: https://youtu.be/JC0DUsq89kw?si=i5JX1YyYoAuBELgr
Download illustration & portrait photos: https://datashare.tu-dresden.de/s/mgFoM9Qf9oAT5Qn

‘Strange metal’ is strangely quiet in noise experiment

Rice physicists find evidence of exotic charge transport in quantum material

Peer-Reviewed Publication

RICE UNIVERSITY

HOUSTON – (Nov. 23, 2023) – True to form, a “strange metal” quantum material proved strangely quiet in recent quantum noise experiments at Rice University. Published this week in Science, the measurements of quantum charge fluctuations known as “shot noise” provide the first direct evidence that electricity seems to flow through strange metals in an unusual liquidlike form that cannot be readily explained in terms of quantized packets of charge known as quasiparticles.

“The noise is greatly suppressed compared to ordinary wires,” said Rice’s Douglas Natelson, the study’s corresponding author. “Maybe this is evidence that quasiparticles are not well-defined things or that they’re just not there and charge moves in more complicated ways. We have to find the right vocabulary to talk about how charge can move collectively.”

The experiments were performed on nanoscale wires of a quantum critical material with a precise 1-2-2 ratio of ytterbium, rhodium and silicon (YbRh2Si2), which has been studied in great depth during the past two decades by Silke Paschen, a solid-state physicist at the Vienna University of Technology (TU Wien). The material contains a high degree of quantum entanglement that produces a very unusual (“strange”) temperature-dependent behavior that is very different from the one in normal metals such as silver or gold.

In such normal metals, each quasiparticle, or discrete unit, of charge is the product of incalculable tiny interactions between countless electrons. First put forward 67 years ago, the quasiparticle is a concept physicists use to represent the combined effect of those interactions as a single quantum object for the purposes of quantum mechanical calculations.

Some prior theoretical studies have suggested that the charge in a strange metal might not be carried by such quasiparticles, and shot noise experiments allowed Natelson, study lead author Liyang Chen, a former student in Natelson’s lab, and other Rice and TU Wien co-authors to gather the first direct empirical evidence to test the idea.

“The shot noise measurement is basically a way of seeing how granular the charge is as it goes through something,” Natelson said. “The idea is that if I’m driving a current, it consists of a bunch of discrete charge carriers. Those arrive at an average rate, but sometimes they happen to be closer together in time, and sometimes they’re farther apart.”

Applying the technique in YbRh2Si2 crystals presented significant technical challenges. Shot noise experiments cannot be performed on single macroscopic crystals but, rather, require samples of nanoscopic dimensions. Thus, the growth of extremely thin but nevertheless perfectly crystalline films had to be achieved, something that Paschen, Maxwell Andrews and their collaborators at TU Wien managed after almost a decade of hard work. Next, Chen had to find a way to maintain that level of perfection while fashioning wires from these thin films that were about 5,000 times narrower than a human hair.

Rice co-author Qimiao Si, the lead theorist on the study and the Harry C. and Olga K. Wiess Professor of Physics and Astronomy, said he, Natelson and Paschen first discussed the idea for the experiments while Paschen was a visiting scholar at Rice in 2016. Si said the results are consistent with a theory of quantum criticality he published in 2001 that he has continued to explore in a nearly two-decade collaboration with Paschen.

“The low shot noise brought about fresh new insights into how the charge-current carriers entwine with the other agents of the quantum criticality that underlies the strange metallicity,” said Si, whose group performed calculations that ruled out the quasiparticle picture. “In this theory of quantum criticality, the electrons are pushed to the verge of localization, and the quasiparticles are lost everywhere on the Fermi surface.”

Natelson said the larger question is whether similar behavior might arise in any or all of the dozens of other compounds that exhibit strange metal behavior.

“Sometimes you kind of feel like nature is telling you something,” Natelson said. “This ‘strange metallicity’ shows up in many different physical systems, despite the fact that the microscopic, underlying physics is very different. In copper-oxide superconductors, for example, the microscopic physics is very, very different than in the heavy-fermion system we’re looking at. They all seem to have this linear-in-temperature resistivity that’s characteristic of strange metals, and you have to wonder is there something generic going on that is independent of whatever the microscopic building blocks are inside them.”

The research was supported by the Department of Energy’s Basic Energy Sciences program (DE-FG02-06ER46337), the National Science Foundation (1704264, 2220603), the European Research Council (101055088), the Austrian Science Fund (FWF I4047, FWF SFB F 86), the Austrian Research Promotion Agency (FFG 2156529, FFG 883941), the European Union’s Horizon 2020 program (824109-EMP), the Air Force Office of Scientific Research (FA8665-22-1-7170), the Welch Foundation (C-1411) and the Vannevar Bush Faculty Fellowship (ONR-VB-N00014-23-1-2870).

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This release was authored by Jade Boyd and can be found online at news.rice.edu.

Follow Rice News and Media Relations via Twitter @RiceUNews.

Peer-reviewed paper:

“Shot noise in a strange metal” | Science | DOI: 10.1126/science.abq6100

Authors: Liyang Chen, Dale T. Lowder, Emine Bakali, Aaron M. Andrews, Werner Schrenk, Monika Waas, Robert Svagera, Gaku Eguchi, Lukas Prochaska, Yiming Wang, Chandan Setty, Shouvik Sur, Qimiao Si, Silke Paschen and Douglas Natelson

https://doi.org/10.1126/science.abq6100

Image downloads:

https://news-network.rice.edu/news/files/2023/11/Doug-and-Liyang-at-defense.jpg
CAPTION: Physicists Liyang Chen (left) and Doug Natelson. (Photo courtesy of D. Natelson/Rice University)

https://news-network.rice.edu/news/files/2023/11/231113_Natelson_Fitlow_018.jpg
CAPTION: Rice University physicist Doug Natelson. (Photo by Jeff Fitlow/Rice University)

https://news-network.rice.edu/news/files/2023/11/1123_SHOTNOISE-spqm8-lg.jpg
CAPTION: Physicists Silke Paschen (left) of Vienna University of Technology and Qimiao Si of Rice University. (Photo by Tommy LaVergne/Rice University)

JOURNAL

Science

DOI

10.1126/science.abq6100

METHOD OF RESEARCH

Experimental study

ARTICLE TITLE

Shot noise in a strange metal

ARTICLE PUBLICATION DATE

23-Nov-2023

LA REVUE GAUCHE - Left Comment

Saturday, November 25, 2023