Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Self-Destructive Effects of Magnetically-Doped Ferromagnetic Topological Insulators

20.01.2015

Magnetic atoms that create exotic surface property also sow the seeds of its destruction

The discovery of "topologically protected" electrical conductivity on the surface of some materials whose bulk interior acts as an insulator was among the most sensational advances in the last decade of condensed matter physics—with predictions of numerous unusual electronic states and new potential applications. But many of these predicted phenomena have yet to be observed.


PNAS

Topographic image of chromium dopant-atom locations at the topological insulator surface.

Now, a new atomic-scale study of the surface properties of one of these ferromagnetic topological insulators reveals that these materials may not be what they had seemed.

The research—conducted at the U.S. Department of Energy's Brookhaven National Laboratory and published in the Early Edition of the Proceedings of the National Academy of Sciences—revealed extreme disorder in a fundamental property of the surface electrons known as the "Dirac mass."

Like the mass imparted to fundamental particles by their interactions with the recently confirmed Higgs field, Dirac mass results from surface particles' interactions with magnetic fields. These fields are created by the presence of magnetic atoms substituted into the material's crystal lattice to convert it into a ferromagnetic topological insulator.

"What we have discovered is that the Dirac mass is extremely disordered at the nanoscale, which was completely unanticipated," said J.C. Séamus Davis, a senior physicist at Brookhaven Lab and a professor at Cornell University and St. Andrew's University in Scotland, who led the research. "The analogous situation in elementary particles would be if the Higgs field was random throughout space so that the electron mass (and the mass of a car or a person) was randomly different at every location. It would be an extremely chaotic universe!"

In the ferromagnetic topological insulators, Davis said, the chaos eventually destroys the exotic surface state.

"Our findings explain why many of the electronic phenomena expected to be present in ferromagnetic topological insulators are in fact suppressed by the very atoms that generate this state, and offer insight into the true atomic-scale mechanism by which the observed properties arise," Davis said. "This new understanding will likely result in revisions of the basic research directions in this field."

Precision studies

Under Davis' guidance, Brookhaven Lab postdoctoral fellows Inhee Lee and Chung Koo Kim studied nearly perfect ferromagnetic topological insulator crystals grown by Brookhaven physicist Genda Gu. They used a spectroscopic imaging, scanning tunneling microscope (SI-STM) designed and built by Davis at Brookhaven to scan the surface of these crystals atom-by-atom. This tool has the precision to simultaneously reveal the positions of the magnetic dopant atoms and the resulting Dirac mass.

Prior to this work, scientists had assumed that these magnetic dopant atoms were not detrimental to the topological surface states. But no one had directly studied how the spatial arrangements of the magnetic dopant atoms at the atomic scale influenced the Dirac-mass because there were no reliable techniques to do so, until now.

The new atom-by-atom SI-STM data revealed not only the intense nanoscale disorder in the Dirac mass, but also showed that this disorder is directly related to fluctuations in the density of the magnetic dopant atoms on different parts of the crystal surface. In the paper, the scientists also provide the first direct evidence for the actual mechanism of how surface ferromagnetism arises in a topological insulator, and determine directly the strength of the surface-state magnetic-dopant interactions.

"The Dirac-mass 'gapmap' technique introduced here reveals radically new perspectives on the physics of ferromagnetic topological insulators," Davis said.

"The key realization from these discoveries—aside from a clear and direct picture of what is going on at the atomic scale—is that, in ferromagnetic topological insulators dominated by this magnetic-dopant atom phenomena, many of the exotic and potentially valuable phenomena expected for these materials are actually being quantum mechanically short circuited by the random variations of Dirac mass," he said.

Of course, there may still be a way to achieve all the exotic physics expected of ferromagnetic topological insulators—if scientists can develop ways to control the dopant-induced Dirac-mass gap disorder. Hence the idea of a whole new research direction for this field.

This research was funded by the DOE Office of Science.

Brookhaven National Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Brookhaven Lab also builds and operates major scientific facilities available to university, industry and government researchers. Brookhaven is operated and managed for DOE's Office of Science by Brookhaven Science Associates, a limited-liability company founded by the Research Foundation for the State University of New York on behalf of Stony Brook University, the largest academic user of Laboratory facilities, and Battelle, a nonprofit applied science and technology organization.

Contact Information
Karen McNulty Walsh
Public Affairs Specialist
kmcnulty@bnl.gov

Karen McNulty Walsh | newswise
Further information:
http://www.bnl.gov

More articles from Physics and Astronomy:

nachricht Ultra-compact phase modulators based on graphene plasmons
27.06.2017 | ICFO-The Institute of Photonic Sciences

nachricht Smooth propagation of spin waves using gold
26.06.2017 | Toyohashi University of Technology

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Touch Displays WAY-AX and WAY-DX by WayCon

27.06.2017 | Power and Electrical Engineering

Drones that drive

27.06.2017 | Information Technology

Ultra-compact phase modulators based on graphene plasmons

27.06.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>