For years, a new synthesis method has been developed at TU Wien (Vienna) to unlock the secrets of “strange metals”. Now a breakthrough has been achieved.
Superconductors allow electrical current to flow without any resistance – but only below a certain critical temperature. Many materials have to be cooled down to almost absolute zero, while some materials keep their superconducting properties up to much higher temperatures. How this “high-temperature superconductivity” works and how it is possible to develop new materials that are superconductors even at normal room temperature is still one of the great mysteries of modern physics.
The key to success could be research on “strange metals”. These are special materials whose electrical resistance shows a very unusual temperature behaviour. This phenomenon is closely related to superconductivity: many classes of high-temperature superconductors exhibit this “strange metal” behavior. Now there has been a major breakthrough: a research team from the TU Wien (Vienna, Austria) and Rice University (Houston, Texas) has developed a new process that allows extremely thin layers of such materials to be produced and then optically analyzed. In this way, important data about these materials are obtained that cannot be measured otherwise, which may lead to the development of better materials and new theories of high-temperature superconductivity.
Strange Metals as the Key to Superconductivity
“Already in 1987, the Nobel Prize in Physics was awarded for the discovery of high-temperature superconductivity, but even today our understanding of this phenomenon is still poor”, says Prof. Silke Bühler-Paschen from the Institute of Solid State Physics at Vienna University of Technology. “However, we know that strange metals are closely related to this technologically important class of superconductors.” Above their critical temperature, high-temperature superconductors show a relationship between temperature and resistance that is completely different from that of ordinary metals. “In contrast to simple metals such as copper or gold, the electrical resistance in strange metals does not appear to be caused by the thermal motion of the atoms, but by certain quantum fluctuations,” says Bühler-Paschen.
To confirm this assumption and to find out more about the nature of quantum fluctuations, not only the temperature dependence of the resistance, but also its frequency dependence must be investigated. The best way to do this is irradiating the material with light in the appropriate frequency range.
A material made of ytterbium, rhodium and silicon (YbRh2Si2), which is known for its particularly pronounced “strange metal” behaviour, was selected for the investigations. To study this material, radiation in the terahertz range is required.
“At this point, things became technologically challenging,” says Silke Bühler-Paschen. “High-precision measurements are only possible in transmission, that is, when the material is penetrated by the terahertz radiation. While electrically insulating materials usually allow terahertz radiation to pass, metals strongly reflect and absorb this type of radiation. Only if an extremely thin layer of the material is available, sufficient terahertz radiation will pass and thus enable precise measurements.”
Developing a New Manufacturing Process
In the clean room laboratories at TU Wien, a new complex molecular beam epitaxy process was developed to produce thin layers of this material: “Ytterbium, rhodium and silicon are evaporated in precisely the right ratio. Atom by atom, these materials impinge on a substrate,” says Maxwell Andrews (Institute for Solid State Electronics, TU Vienna). “If all parameters are set correctly, YbRh2Si2 grows in atomic layers. By choosing the right duration of the growth process, you can achieve exactly the desired layer thickness.”
“The decisive breakthrough was finding a perfectly fitting substrate on which to apply these layers – namely germanium,” says Lukas Prochaska, one of the three leading doctoral students in the team. “The crystal structure of germanium fits geometrically perfectly the arrangement of the Ytterbium atoms. This allowed us to grow thin films of excellent quality.”
Understanding the Movement of Charge Carriers
PhD student Xinwei Li in the Kono group at Rice University then performed challenging high-precision tetahertz measurements on the thin films. The analysis of the data, in which Rice theorist Qimiao Si also played a major role, yielded decisive new evidence: “Our assumption that quantum-critical charge fluctuations play an important role has now been confirmed,” says Silke Bühler-Paschen. “We have come full circle here: In 2004, we were able to show that the “strange metal” behavior in this material is accompanied by a sudden change in the charge carrier concentration. At that time, Qimiao Si and I had already recognized the need for dynamical measurements, but the technology to realize them was not available. Now we were finally able to scrutinize and understand this process.”
The new results indicate how to describe these unusual material effects. “Our new ideas can also be transferred to other classes of high-temperature superconductors,” explains Bühler-Paschen. “We hope that this will lead to a new theory of high-temperature superconductivity, and to the design of better superconductors with even higher critical temperatures; this would be a tremendous technological success.”
NAIROBI, Kenya (AP) — The body of Ugandan Olympic athlete Rebecca Cheptegei — who died after being set on fire by her partner in Kenya — was received Friday by family and anti-femicide crusaders, ahead of her burial a day later.
Cheptegei’s family met with dozens of activists Friday who had marched to the Moi Teaching and Referral Hospital’s morgue in the western city of Eldoret while chanting anti-femicide slogans.
She is the fourth female athlete to have been killed by her partner in Kenya in yet another case of gender-based violence in recent years.
Viola Cheptoo, the founder of Tirop Angels – an organization that was formed in honor of athlete Agnes Tirop, who was stabbed to death in 2021, said stakeholders need to ensure this is the last death of an athlete due to gender-based violence.
“We are here to say that enough is enough, we are tired of burying our sisters due to GBV,” she said.
It was a somber mood at the morgue as athletes and family members viewed Cheptegei’s body which sustained 80% of burns after she was doused with gasoline by her partner Dickson Ndiema. Ndiema sustained 30% burns on his body and later succumbed.
Ndiema and Cheptegei were said to have quarreled over a piece of land that the athlete bought in Kenya, according to a report filed by the local chief.
Cheptegei competed in the women’s marathon at the Paris Olympics less than a month before the attack. She finished in 44th place.
Cheptegei’s father, Joseph, said that the body will make a brief stop at their home in the Endebess area before proceeding to Bukwo in eastern Uganda for a night vigil and burial on Saturday.
“We are in the final part of giving my daughter the last respect,” a visibly distraught Joseph said.
He told reporters last week that Ndiema was stalking and threatening Cheptegei and the family had informed police.
Four in 10 women or an estimated 41% of dating or married Kenyan women have experienced physical or sexual violence perpetrated by their current or most recent partner, according to the Kenya Demographic and Health Survey 2022.
TEL AVIV, Israel (AP) — A rare Bronze-Era jar accidentally smashed by a 4-year-old visiting a museum was back on display Wednesday after restoration experts were able to carefully piece the artifact back together.
Last month, a family from northern Israel was visiting the museum when their youngest son tipped over the jar, which smashed into pieces.
Alex Geller, the boy’s father, said his son — the youngest of three — is exceptionally curious, and that the moment he heard the crash, “please let that not be my child” was the first thought that raced through his head.
The jar has been on display at the Hecht Museum in Haifa for 35 years. It was one of the only containers of its size and from that period still complete when it was discovered.
The Bronze Age jar is one of many artifacts exhibited out in the open, part of the Hecht Museum’s vision of letting visitors explore history without glass barriers, said Inbal Rivlin, the director of the museum, which is associated with Haifa University in northern Israel.
It was likely used to hold wine or oil, and dates back to between 2200 and 1500 B.C.
Rivlin and the museum decided to turn the moment, which captured international attention, into a teaching moment, inviting the Geller family back for a special visit and hands-on activity to illustrate the restoration process.
Rivlin added that the incident provided a welcome distraction from the ongoing war in Gaza. “Well, he’s just a kid. So I think that somehow it touches the heart of the people in Israel and around the world,“ said Rivlin.
Roee Shafir, a restoration expert at the museum, said the repairs would be fairly simple, as the pieces were from a single, complete jar. Archaeologists often face the more daunting task of sifting through piles of shards from multiple objects and trying to piece them together.
Experts used 3D technology, hi-resolution videos, and special glue to painstakingly reconstruct the large jar.
Less than two weeks after it broke, the jar went back on display at the museum. The gluing process left small hairline cracks, and a few pieces are missing, but the jar’s impressive size remains.
The only noticeable difference in the exhibit was a new sign reading “please don’t touch.”
VICTORIA – The British Columbia government is partnering with a bear welfare group to reduce the number of bears being euthanized in the province.
Nicholas Scapillati, executive director of Grizzly Bear Foundation, said Monday that it comes after months-long discussions with the province on how to protect bears, with the goal to give the animals a “better and second chance at life in the wild.”
Scapillati said what’s exciting about the project is that the government is open to working with outside experts and the public.
“So, they’ll be working through Indigenous knowledge and scientific understanding, bringing in the latest techniques and training expertise from leading experts,” he said in an interview.
B.C. government data show conservation officers destroyed 603 black bears and 23 grizzly bears in 2023, while 154 black bears were killed by officers in the first six months of this year.
Scapillati said the group will publish a report with recommendations by next spring, while an independent oversight committee will be set up to review all bear encounters with conservation officers to provide advice to the government.
Environment Minister George Heyman said in a statement that they are looking for new ways to ensure conservation officers “have the trust of the communities they serve,” and the panel will make recommendations to enhance officer training and improve policies.
Lesley Fox, with the wildlife protection group The Fur-Bearers, said they’ve been calling for such a committee for decades.
“This move demonstrates the government is listening,” said Fox. “I suspect, because of the impending election, their listening skills are potentially a little sharper than they normally are.”
Fox said the partnership came from “a place of long frustration” as provincial conservation officers kill more than 500 black bears every year on average, and the public is “no longer tolerating this kind of approach.”
“I think that the conservation officer service and the B.C. government are aware they need to change, and certainly the public has been asking for it,” said Fox.
Fox said there’s a lot of optimism about the new partnership, but, as with any government, there will likely be a lot of red tape to get through.
“I think speed is going to be important, whether or not the committee has the ability to make change and make change relatively quickly without having to study an issue to death, ” said Fox.
This report by The Canadian Press was first published Sept. 9, 2024.
