XAOS THEORY
Noise – not a nuisance but a source of information
Researchers at the University of Konstanz discover a new type of ultrafast magnetic switching by investigating fluctuations that normally tend to interfere with experiments as noise
Noise on the radio when reception is poor is a typical example of how fluctuations mask a physical signal. In fact, such interference or noise occurs in every physical measurement in addition to the actual signal. "Even in the loneliest place in the universe, where there should be nothing at all, there are still fluctuations of the electromagnetic field", says physicist Ulrich Nowak. In the Collaborative Research Centre (CRC) 1432 "Fluctuations and Nonlinearities in Classical and Quantum Matter beyond Equilibrium" at the University of Konstanz, researchers do not see this omnipresent noise as a disturbing factor that needs to be eliminated as far as possible, but as a source of information that tells us something about the signal.
No magnetic effect, but fluctuations
This approach has now proved successful when investigating antiferromagnets. Antiferromagnets are magnetic materials in which the magnetizations of several sub-lattices cancel out each other. Nevertheless, antiferromagnetic insulators are considered promising for energy-efficient components in the field of information technology. As they have hardly any magnetic fields on the outside, they are very difficult to characterize physically. Yet, antiferromagnets are surrounded by magnetic fluctuations, which can tell us a lot about this weakly magnetic material.
In this spirit, the groups of the two materials scientists Ulrich Nowak and Sebastian Gönnenwein analysed the fluctuations of antiferromagnetic materials in the context of the CRC. The decisive factor in their theoretical as well as experimental study, recently published in the journal Nature Communications, was the specific frequency range. "We measure very fast fluctuations and have developed a method with which fluctuations can still be detected on the ultrashort time scale of femtoseconds", says experimental physicist Sebastian Gönnenwein. A femtosecond is one millionth of a billionth of a second.
New experimental approach for ultrafast time scales
On slower time scales, one could use electronics that are fast enough to measure these fluctuations. On ultrafast time scales, this no longer works, which is why a new experimental approach had to be developed. It is based on an idea from the research group of Alfred Leitenstorfer, who is also a member of the Collaborative Research Centre. Employing laser technology, the researchers use pulse sequences or pulse pairs in order to obtain information about fluctuations. Initially, this measurement approach was developed to investigate quantum fluctuations, and has now been extended to fluctuations in magnetic systems. Takayuki Kurihara from the University of Tokyo played a key role in this development as the third cooperation partner. He was a member of the Leitenstorfer research group and the Zukunftskolleg at the University of Konstanz from 2018 to 2020.
Detection of fluctuations using ultrashort light pulses
In the experiment, two ultrashort light pulses are transmitted through the magnet with a time delay, testing the magnetic properties during the transit time of each pulse, respectively. The light pulses are then checked for similarity using sophisticated electronics. The first pulse serves as a reference, the second contains information about how much the antiferromagnet has changed in the time between the first and second pulse. Different measurement results at the two points of time confirm the fluctuations. Ulrich Nowak's research group also modelled the experiment in elaborate computer simulations in order to better understand its results.
One unexpected result was the discovery of what is known as telegraph noise on ultrashort time scales. This means that there is not only unsorted noise, but also fluctuations in which the system switches back and forth between two well-defined states. Such fast, purely random switching has never been observed before and could be interesting for applications such as random number generators. In any case, the new methodological possibilities for analyzing fluctuations on ultrashort time scales offer great potential for further discoveries in the field of functional materials.
Key facts:
- Original publication: M. A. Weiss, A. Herbst, J. Schlegel, T. Dannegger, M. Evers, A. Donges, M. Nakajima, A. Leitenstorfer, S. T. B. Goennenwein, U. Nowak & T. Kurihara: Discovery of ultrafast spontaneous spin switching in an antiferromagnet by femtosecond noise correlation spectroscopy. Nat Commun 14, 7651 (2023). https://doi.org/10.1038/s41467-023-43318-8
- By studying fluctuations, researchers at the University of Konstanz discover a new type of magnetic switching
- Project cooperation between materials scientists Professor Alfred Leitenstorfer, Professor Ulrich Nowak and Professor Sebastian Gönnenwein from the University of Konstanz, Associate Professor Makoto Nakajima from Osaka University and Dr. Takayuki Kurihara from the University of Tokyo
- The study was funded by the Collaborative Research Centre 1432.
You can download images here:
https://www.uni-konstanz.de/fileadmin/pi/fileserver/2023/rauschen_sns.jpg
Caption:
Testing the ultrafast fluctuations of the magnetic moments in an antiferromagnet with two laser pulses transmitted with a time delay.
Copyright: Julius Schlegel/University of Konstanz
https://www.uni-konstanz.de/fileadmin/pi/fileserver/2023/rauschen_rtn.jpg
Caption:
What is known as telegraph noise occurs when the magnetic moments in antiferromagnets switch back and forth between two well-defined states.
Copyright: Marvin Weiss/University of Konstanz
JOURNAL
Nature Communications
DOI
Loss of auditory nerve fibers uncovered in individuals with tinnitus
Mass Eye and Ear researchers link tinnitus to auditory nerve degeneration in individuals with a normal hearing test
IMAGE:
STÉPHANE F. MAISON, PHD, CCC-A, AN INVESTIGATOR AT MASS EYE AND EAR'S EATON-PEABODY LABORATORIES, AND CLINICAL DIRECTOR OF THE TINNITUS CENTER AT MASS EYE AND EAR.
view moreCREDIT: MASS EYE AND EAR
A new study from Mass Eye and Ear investigators shows that individuals who report tinnitus, which present as a ringing in the ears in more than one out of ten adults worldwide, are experiencing auditory nerve loss that is not picked up by conventional hearing tests. This work is part of a P50 grant awarded by the National Institutes of Health (NIH) to Mass Eye and Ear researchers within the Eaton-Peabody Laboratories (EPL) for their work on cochlear synaptopathy, which is commonly referred to as “hidden hearing loss.” The results from this study provide a better understanding on the origins of tinnitus and are published November 30th in Scientific Reports.
“Beyond the nuisance of having persistent ringing or other sounds in the ears, tinnitus symptoms are debilitating in many patients, causing sleep deprivation, social isolation, anxiety and depression, adversely affecting work performance, and reducing significantly their quality of life,” said senior author Stéphane F. Maison, PhD, CCC-A, a principal investigator at Mass Eye and Ear, a member of Mass General Brigham, and clinical director of the Mass Eye and Ear Tinnitus Clinic. “We won’t be able to cure tinnitus until we fully understand the mechanisms underlying its genesis. This work is a first step toward our ultimate goal of silencing tinnitus.”
Many individuals with hearing loss report a buzzing, humming, ringing or even roaring sound in their ears. It’s been a longstanding idea that these symptoms, known as tinnitus, arise as a result of a maladaptive plasticity of the brain. In other words, the brain tries to compensate for the loss of hearing by increasing its activity, resulting in the perception of a phantom sound, tinnitus. Until recently though, this idea was disputed as some tinnitus sufferers have normal hearing tests.
However, the discovery of cochlear synaptopathy back in 2009 by Mass Eye and Ear investigators brought back to life this hypothesis as it was evidenced that patients with a normal hearing test can have a significant loss to the auditory nerve. In view of this paradigm shift in the way researchers and clinicians think about hearing loss, Maison and his team sought to determine if such hidden damage could be associated with the tinnitus symptoms experienced by a cohort of normal hearing participants. By measuring the response of their auditory nerve and brainstem, the researchers found that chronic tinnitus was not only associated with a loss of auditory nerve but that participants showed hyperactivity in the brainstem.
“Our work reconciles the idea that tinnitus may be triggered by a loss of auditory nerve, including in people with normal hearing,” said Maison.
In terms of future directions, the investigators aim to capitalize on recent work geared toward the regeneration of auditory nerve via the use of drugs called neurotrophins.
“The idea that, one day, researchers might be able to bring back the missing sound to the brain and, perhaps, reduce its hyperactivity in conjunction with retraining, definitely brings the hope of a cure closer to reality”, Maison added.
Disclosures: The authors declare no competing interests.
Funding: This work was supported by a grant from the NIDCD (P50 DC015857) and the Lauer Tinnitus Research Center at the Mass Eye and Ear.
Paper cited: Vasilkov, V et al. “Evidence of cochlear neural degeneration in normal-hearing subjects with tinnitus” Scientific Reports DOI: 10.1038/s41598-023-46741-5
###
About Mass Eye and Ear
Massachusetts Eye and Ear, founded in 1824, is an international center for treatment and research and a teaching hospital of Harvard Medical School. A member of Mass General Brigham, Mass Eye and Ear specializes in ophthalmology (eye care) and otolaryngology–head and neck surgery (ear, nose and throat care). Mass Eye and Ear clinicians provide care ranging from the routine to the very complex. Also home to the world's largest community of hearing and vision researchers, Mass Eye and Ear scientists are driven by a mission to discover the basic biology underlying conditions affecting the eyes, ears, nose, throat, head and neck and to develop new treatments and cures. In the 2023–2024 “Best Hospitals Survey,” U.S. News & World Report ranked Mass Eye and Ear #4 in the nation for eye care and #7 for ear, nose and throat care. For more information about life-changing care and research at Mass Eye and Ear, visit our blog, Focus, and follow us on Instagram, Twitter and Facebook.
JOURNAL
Scientific Reports
METHOD OF RESEARCH
Experimental study
SUBJECT OF RESEARCH
People
ARTICLE TITLE
Evidence of cochlear neural degeneration in normal-hearing subjects with tinnitus
ARTICLE PUBLICATION DATE
30-Nov-2023
No comments:
Post a Comment