Magnetic effect without a magnet
Surprise in solid-state physics: The Hall effect, which normally requires magnetic fields, can also be generated in a completely different way -- with extreme strength
2021-02-22
(Press-News.org) Electric current is deflected by a magnetic field - in conducting materials this leads to the so-called Hall effect. This effect is often used to measure magnetic fields. A surprising discovery has now been made at TU Wien, in collaboration with scientists from the Paul Scherrer Institute (Switzerland), McMater University (Canada), and Rice University (USA): an exotic metal made of cerium, bismuth and palladium was examined and a giant Hall effect was found to be produced by the material, in the total absence of any magnetic field. The reason for this unexpected result lies in the unusual properties of the electrons: They behave as if magnetic monopoles were present in the material. These discoveries have now been published in the scientific magazine PNAS.
A voltage perpendicular to the current
When an electric current flows through a metal strip, electrons move from one side to the other. If a magnet is placed next to this strip, a force acts on the electrons - the so-called Lorentz force. The path of the electrons through the metal strip is no longer straight, it is bent a little. Therefore, there are now more electrons on one side of the metal strip than on the other, and this creates a voltage - perpendicular to the direction in which the current flows. This is the classic Hall effect, as it has been known for many years.
"Measuring the strength of the Hall effect is one of the ways we characterise materials in our laboratory," says Prof. Silke Bühler-Paschen from the Institute of Solid State Physics at TU Wien. "You can learn a lot about the behaviour of electrons in the solid state from such an experiment." When Sami Dzsaber, who was working on his dissertation in Bühler-Paschen's research group, examined the material Ce3Bi4Pd3, he took his task very seriously and also carried out a measurement without a magnetic field. "Actually, this is an unusual idea - but in this case it was the decisive step", says Silke Bühler-Paschen.
The measurement revealed that the material exhibits a Hall effect even without an external magnetic field - and not just a normal Hall effect, but a huge one. In normal materials, a Hall effect of this strength can only be produced with enormous electromagnetic coils. "So we had to answer another question," says Silke Bühler Paschen. "If a Hall effect occurs without an external magnetic field, are we perhaps dealing with extremely strong local magnetic fields that occur on a microscopic scale inside the material, but can no longer be felt outside?"
Investigations were therefore carried out at the Paul Scherrer Institute in Switzerland: With the help of muons - elementary particles that are particularly well suited for investigating magnetic phenomena - the material was examined more closely. But it turned out that no magnetic field could be detected even on a microscopic scale. "If there is no magnetic field, then there is also no Lorentz force that can act on the electrons in the material - but nevertheless a Hall effect was measured. That is really remarkable," says Silke Bühler-Paschen.
Symmetry is what counts
The explanation for this strange phenomenon lies in the complicated interaction of the electrons. "The atoms of this material are arranged according to very specific symmetries, and these symmetries determine the so-called dispersion relation - that is the relationship between the energy of the electrons and their momentum. The dispersion relation tells us how fast an electron can move when it has a certain energy," says Bühler-Paschen. "It's also important to note that you can't look at the electrons individually here - there are strong quantum mechanical interactions between them."
This complex interaction results in phenomena that mathematically look as if there are magnetic monopoles in the material - i.e. solitary north and south poles, which do not exist in this form in nature. "But it actually has the effect of a very strong magnetic field on the movement of the electrons," says Bühler-Paschen.
The effect had already been predicted theoretically for simpler materials, but no one had been able to prove it. The breakthrough came with the investigation of a new class of materials: "Our material with the chemical composition Ce3Bi4Pd3 is characterised by a particularly strong interaction between the electrons," explains Bühler-Paschen. "This is known as the Kondo effect. It causes these fictitious magnetic monopoles to have exactly the right energy to influence the conduction electrons in the material extremely strongly. This is the reason why the effect is more than a thousand times larger than theoretically predicted."
The new giant spontaneous Hall effect holds some potential for next-generation quantum technologies. In this field, for example, non-reciprocal elements that produce direction-dependent scattering entirely without an external magnetic field are of importance; they could be realized with this effect. "The extremely non-linear behaviour of the material is also of great interest," says Silke Bühler-Paschen. "The fact that complex many-particle phenomena in solids give rise to unexpected application possibilities makes this field of research particularly exciting."
INFORMATION:
Contact
Prof. Silke Bühler-Paschen
Institute for Solid State Physics
TU Wien
Wiedner Hauptstraße 8-10, 1040 Vienna
+43 1 58801 13716
silke.buehler-paschen@tuwien.ac.at
[Attachments] See images for this press release:
ELSE PRESS RELEASES FROM THIS DATE:
2021-02-22
The pituitary gland is a pea-sized endocrine gland composed of two structurally and functionally separate parts known as anterior and posterior lobes. The pituitary gland's anterior lobe secretes six hormones essential to growth, reproduction, and other basic physiological functions. Abnormal development of the pituitary gland, or hypopituitarism, can cause mild or complete deficiency of one or more pituitary hormones, which manifests as highly varying symptoms. Tumours mainly cause hypopituitarism in humans, but a congenital factor can also be associated with the disorder.
The POU1F1 gene regulates the development of the ...
2021-02-22
In Sweden, approximately one in five adults suffers from dental anxiety or phobia. The number has decreased over time, but still an important part of the population have major problems, according to a recent doctoral thesis from the University of Gothenburg.
The thesis includes a nationwide interview study involving 3,500 adult individuals, randomly selected from the general population of Sweden. Nineteen percent of the participants reported some degree of dental anxiety, fear or phobia.
The results showed that 4.7% of the respondents described their dental anxiety as severe, 4.5% as moderate and 9.8% as low. The remaining 80.9% reported no dental anxiety. The proportion with no dental ...
2021-02-22
Scientists of the P. N. Lebedev Physical Institute of the Russian Academy of Sciences (LPI RAS), the Moscow Institute of Physics and Technology (MIPT) and the Institute for Nuclear Research of RAS (INR RAS) studied the arrival directions of astrophysical neutrinos with energies more than a trillion electronvolts (TeV) and came to an unexpected conclusion: all of them are born near black holes in the centers of distant active galaxies powerful radio sources. Previously, only neutrinos with the highest energies were assumed to be obtained in sources of this class.
It is believed that there are massive black holes in the centers ...
2021-02-22
Invasive lobular carcinoma (ILC) is a type of breast cancer that begins in the milk-producing glands (lobules) of the breast. It covers 10-15% of all breast cancer cases, has a high risk of late recurrence, unique metastatic sites, high sensitivity to hormones, unpredictable responses to therapies, unique histopathology, distinctive biology, and resists chemotherapy. More than 90% of ILC tumors also contain estrogen receptors, meaning that they can receive hormone signals from the body e.g. estradiol, that can spur their growth and metastasis.
Despite all this, ILC is relatively understudied compared to other breast cancers, and as a result, there have been very few models developed to study it. The reason is ...
2021-02-22
Water is an essential element for all living things. Understanding the dynamics of water in trees is crucial for understanding the consequences of climate change and altered water availability for forest ecosystems. This study, which is a product of a joint research project with Samuli Junttila PhD, and Professor Masato Katoh of Shinshu University's Institute for Mountain Science and others demonstrates a new laser scanning based method that can be used to monitor changes in leaf water content of tree communities.
Lasers can be used to measure and monitor the leaf water content of trees and plants, because the reflection of laser light at the shortwave infrared region is changed due to varying leaf water ...
2021-02-22
Two in five of the world's plant species are at risk of extinction. In the face of climate change, understanding why certain plant species are vulnerable to extinction while others prevail is more urgent than ever before. Previous studies linking climate and plant vital rates have found relatively modest effects, sometimes leading to the conclusion that other threats, such as land use change, may still be more important than climate drivers. However, these conclusions could result from wrong assumptions about which times of the year (which "time window") climate ...
2021-02-22
- A silicone membrane for wearable devices is more comfortable and breathable thanks to better-sized pores made with the help of citric acid crystals. -
A new preparation technique fabricates thin, silicone-based patches that rapidly wick water away from the skin. The technique could reduce the redness and itching caused by wearable biosensors that trap sweat beneath them. The technique was developed by bioengineer and professor Young-Ho Cho and his colleagues at KAIST and reported in the journal Scientific Reports last month.
"Wearable bioelectronics are becoming more attractive for the day-to-day monitoring of biological compounds ...
2021-02-22
"The lengthy groundwork is finally complete," says Jouko Rikkinen, Professor of Botany at the University of Helsinki, Finland, giving a sigh of relief.
The research article just published focuses on species diversity in the genus Leptogium, a group of jelly lichens that are common in the mountain forests of East Africa. Thousands of lichen specimens were collected from Kenya and Tanzania in 2009-2017, including nearly 600 Leptogium specimens.
DNA analyses revealed that the dataset on Leptogium included more than 70 different species, of which no more than a dozen or so are previously known. DNA analyses were necessary, as ...
2021-02-22
The course and severity of COVID-19 in individual patients is largely influenced by the interaction between the SARS-CoV-2 coronavirus and the human immune system. Normally, the antiviral immune response of natural killer cells (NK cells) is an important step in combating viral replication in the early phase of the infection. On their surface, these killer cells have special, activating receptors, including the NKG2C receptor, which communicates with an infected cell via one of its specialised surface structures, HLA-E. This interaction results in the destruction of virus-infected cells. However, due to a genetic ...
2021-02-22
Professor Jeremy Michalek and his Ph.D student Matthew Bruchon have published a study investigating what vehicle electrification would look like in a world where ridesourcing companies like Uber and Lyft were held responsible for the air pollution and carbon emissions created by their business.
Ridesourcing has changed the way people travel, affecting air emissions in the process. Researchers like those at the Center for Air, Climate and Energy Solutions (CACES) have quantified the negative health effects of airborne particulates created by cars in rates of cardiovascular and respiratory disease, and they're also the largest source of greenhouse gasses in the US. With public sector fleets such as the US Postal Service ...
LAST 30 PRESS RELEASES:
[Press-News.org] Magnetic effect without a magnet
Surprise in solid-state physics: The Hall effect, which normally requires magnetic fields, can also be generated in a completely different way -- with extreme strength
