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Strange quantum effect found in an exotic superconductor
Researchers discovered a mysterious quantum effect that breaks a 60-year-old physics theorem.
- Princeton scientists lead an international team that discovered unusual behavior in iron-based superconductors.
- The researchers observed how adding cobalt atoms disrupted superconductivity.
- The experiment demonstrated unexpected quantum behavior.
An international team of researchers observed an unexpected quantum effect in an exotic superconductor. Their discovery can lead to the next generation of energy-saving technologies.
Traditional superconductors, used for conducting electricity without resistance, work at low temperatures. However, some iron-based superconductors discovered about a decade ago, work at high temperatures. How they do it has been unclear, especially as the magnetism of iron conflicts with the appearance of superconductivity, explains the press release from Princeton, whose scientists led the research.
Figuring out how these iron-based superconductors operate could open doors to new applications, prompting the focus of researchers. They probed these materials by adding impurities — atoms of cobalt — to see how superconductivity was created and dissipated. Introducing cobalt has been shown to make iron-based superconductors to lose the property of superconductivity. It starts acting like a regular metal, where electrical flow is met with resistance and loss of energy.
The team's leader, M. Zahid Hasan, Professor of Physics at Princeton University, likened their approach to throwing a stone in the water to see how water would react, pointing out "The way the superconducting properties react to the impurity reveals their secrets with quantum-level detail."
Their team employed a technique called scanning tunneling microscopy to image individual atoms in a superconductor made of lithium, iron and arsenic while they added in cobalt atoms. They were able to observe how introducing more cobalt atoms made superconductivity disappear.
What was surprising, the researchers found that the cobalt atoms were able to disrupt electron pairing while replacing iron atoms in the metal. This behavior, which resulted in a quantum phase transition, changing the state from superconducting to non-superconducting, also violated the well-established Anderson's theorem. Proposed in 1959 by the Nobel Prize-winning physicist Philip Anderson, it was the accepted explanation for what would happen if you added impurities to a superconductor. The new research clearly shows an exception to Anderson's theorem.
Another unusual find revealed that the cobalt impurities also transformed the nature and the shape of the so-called "energy gap" - a feature emblematic of superconductivity. The shape of the gap is indicative of the "order parameter" linked to the nature of the superconductivity. The effect on this property is mysterious and points to a sign change in the order parameter's phase.
From left to right: Graduate student Nana Shumiya, Professor M. Zahid Hasan, Postdoctoral Research Associate Jia-Xin Yin and Graduate Student Yuxiao Jiang. Photo by Zijia Cheng
Credit: Princeton University
Postdoctoral researcher Ilya Belopolski, the co-author of the study, explained the significance of the researchers' feat:
"Naively, distinguishing between conventional superconductivity and sign-changing superconductivity requires a phase-sensitive measurement of the superconducting order parameter, which can be extremely challenging," said Belopolski. "A beautiful aspect of our experiment is that by considering violations of Anderson's theorem, we can get around this requirement.
Check out the study published in Physical Review Letters.
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A scientist in Sweden makes a controversial presentation at a future of food conference.
- A behavioral scientist from Sweden thinks cannibalism of corpses will become necessary due to effects of climate change.
- He made the controversial presentation to Swedish TV during a "Future of Food" conference in Stockholm.
- The scientist acknowledges the many taboos this idea would have to overcome.
Depiction of cannibalism in the Medieval ages.
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President Vladimir Putin announces approval of Russia's coronavirus vaccine but scientists warn it may be unsafe.
A new coronavirus vaccine on display at the Nikolai Gamaleya National Center of Epidemiology and Microbiology in Moscow, Russia.
Credit: Alexander Zemlianichenko Jr/ Russian Direct Investment Fund via AP
Medical workers draw blood from volunteers participating in a trial of a coronavirus vaccine at the Budenko Main Military Hospital outside Moscow, Russia.
Credit: Russian Defense Ministry Press Service via AP
A report from the New York Times raises questions over how the teletherapy startup Talkspace handles user data.
- In the report, several former employees said that "individual users' anonymized conversations were routinely reviewed and mined for insights."
- Talkspace denied using user data for marketing purposes, though it acknowledged that it looks at client transcripts to improve its services.
- It's still unclear whether teletherapy is as effective as traditional therapy.
Talkspace.com<p>Former employees also questioned the legitimacy of certain interventions by the company into client-therapist interactions. For example, after one therapist sent a client a link to an online anxiety worksheet, a company representative instructed her to try to keep clients inside the app.</p><p style="margin-left: 20px;">"I was like, 'How do you know I did that?'" Karissa Brennan, a therapist who worked with Talkspace from 2015 to 2017, told the Times. "They said it was private, but it wasn't."</p><p>Other former employees said the company would pay special attention to its "enterprise partner" clients, who worked at companies like Google. One therapist said Talkspace contacted her for taking too long to respond to Google clients.</p><p>Talkspace responded to the Times with a Medium <a href="https://medium.com/@founders_22883/talkspace-founders-respond-to-a-new-york-times-article-78d6f5c45c59" target="_blank">post</a>, which claimed the Times report contained false and "uninformed assertions."</p><p style="margin-left: 20px;">"Talkspace is a HIPAA/HITECH and SOC2 approved platform, audited annually by external vendors, and has deployed additional technologies to keep its data safe, exceeding all existing regulatory requirements," the post states.</p>