While insulating against electrical currents in their interior, the surface of materials called topological insulators permits the flow of electron spins relatively unhindered.
The almost lossless flow of spin information makes topological insulators a promising new class of materials for electronic applications: the electron spins could be harnessed to transmit information in the same way that electrical charges are used in conventional electronics.
Electron spins are also susceptible to magnetic fields, so electrical control of the magnetic fields of these materials would offer further control over the properties of electronic devices. Magnetic impurities in these materials, however, have thwarted attempts by experimental physicists to fabricate topological insulators, because they destroy the characteristic energy structure of a topological insulator.
In a theoretical study, Kentaro Nomura and Naoto Nagaosa from the RIKEN Advanced Science Institute, Wako, have unexpectedly discovered that the electrical control of magnetization in topological insulators is actually enhanced by the presence of magnetic impurities. It may be possible, therefore, to develop novel devices from topological insulators by creating magnetization with electrical fields.
Topological insulators owe their unique properties to time-reversal symmetry: if the flow of time were reversed, the material would behave in the same way. Magnetic impurities break this symmetry, as magnetism is sensitive to time reversal; electrical currents flowing forward and backward in time create magnetic fields pointing in opposite directions. Physicists therefore expected that magnetic impurities would disrupt the magnetization generated by electrical currents on the surface of a topological insulator.
Nomura and Nagaosa’s calculations, however, showed that randomly distributed magnetic impurities do not influence the strong coupling between electrical currents and magnetic fields. Electrical currents at the surface are quantized, which means that they change only in steps. Therefore, a change in the energy structure of the material would not affect the electric current and magnetization. The randomness of the impurities increases the usable energy range, says Nomura. “Usually impurities and disorder smear desired effects. In this case, imperfections enhance them.”
This finding is welcome news for experimental physicists working on topological insulators. All samples fabricated to date contain so many impurities that observing spin currents at their surface is almost impossible. The discovery that magnetic impurities should have no detrimental effect improves the likelihood of observing the proposed control of magnetization. Consequently, says Nomura, “a number of experimental groups are already working on this issue. I think this effect will be observed, hopefully soon.”
The corresponding author for this highlight is based at the Strong-Correlation Theory Research Team, RIKEN Advanced Science InstituteReference:
Chen, Y.L., Chu, J.-H., Analytis, J.G., Liu, Z.K., Igarashi, K., Kuo, H.-H., Qi, X.L., Mo, S.K., Moore, R.G., Lu, D.H., et al. Massive Dirac fermion on the surface of a magnetically doped topological insulator. Science 329, 659–662 (2010).
Organic-inorganic heterostructures with programmable electronic properties
29.03.2017 | Technische Universität Dresden
Researchers use light to remotely control curvature of plastics
23.03.2017 | North Carolina State University
The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.
To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...
Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.
The results will be published on March 22 in the journal „Astronomy & Astrophysics“.
Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...
Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.
Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...
In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.
Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...
20.03.2017 | Event News
14.03.2017 | Event News
07.03.2017 | Event News
29.03.2017 | Materials Sciences
29.03.2017 | Physics and Astronomy
29.03.2017 | Earth Sciences