Three research groups, two kinds of electronic properties, one material

Science Daily  June 10, 2020 An international team of researchers (Israel, Germany) has shown that Bi2TeI (bismuth, tellurium and iodine ) is a dual topological insulator. It exhibits band inversions at two-time reversal symmetry points of the bulk band, which classify it as a weak topological insulator with metallic states on its ‘side’ surfaces. The mirror symmetry of the crystal structure concurrently classifies it as a topological crystalline insulator. They show the existence of both two-dimensional Dirac surface states, which are susceptible to mirror symmetry breaking, and one-dimensional channels that reside along the step edges. Their mutual coexistence on the […]

Molecules with a spin on a topological insulator: a hybrid approach to magnetic topological states of matter

Nanowerk  April 29, 2020 Controlling the interactions at the interface of a magnetic/topological insulator heterostructure is an outstanding challenge with implications in fundamental science and technology. An international team of researchers (Spain, Switzerland, Italy) has shown that it is possible to tune the interfacial interaction without quenching the molecular spin and the topological surface state of the topological insulator by choosing suitable organic ligands. They found that CoTBrPP and CoPc monolayers (metal-organic molecules) adsorbed on Bi2Te3 (topological insulator) form robust interfaces where electronic interactions can be tuned without strongly perturbing the intrinsic properties of each constituent. Their conclusions are supported […]

Scientists discover first antiferromagnetic topological quantum material

Science Daily  December 19, 2019 An international team of researchers led by Spain has developed a crystal growing technique for intrinsically magnetic topological material manganese-bismuth telluride (MnBi2Te4) and characterized the physical properties of the crystals. The team was able to prove both in theory and in spectroscopic experiments that MnBi2Te4 is the first antiferromagnetic topological insulator (AFMTI) below its Néel temperature. They optimized the synthesis protocol for the new material so that MnBi2Te4 single crystals can be produced more easily. Recent findings show that there are even more structural derivatives of MnBi2Te4, which are relevant in the context of MTI…read […]

Mind the gap – new wide-bandgap topological insulator

Nanowerk  December 17, 2019 To construct electronic devices with low-energy consumption the low-dissipation surface states of topological insulators (TIs) are widely employed. But practical applications of TIs have been severely limited by the small electronic bandgaps in most known materials. To achieve stability researchers in Australia used a scheme based on co-substitution of sulphur balanced by a small amount of larger vanadium and tin ions resulting the complex material Vx:Bi1.08-xSn0.02Sb0.9Te2S. They demonstrated that the surface dominant transport behavior can survive above 50 K. The robust surface states in V doped single crystal systems provide an ideal platform to study the Dirac […]

New topological insulator reroutes photonic ‘traffic’ on the fly   September 13, 2019 An international team of researchers (USA – University of Pennsylvania, Italy) has developed a prototype photonic chip that is roughly 250 microns square and features a tessellated grid of oval rings. By pumping the chip with an external laser, targeted to alter the photonic properties of individual rings, they are able to alter which of those rings constitute the boundaries of a waveguide. The result is a reconfigurable topological insulator. By changing the pumping patterns, photons headed in different directions can be routed around each other, allowing photons from multiple data packets to travel through the […]

Scientists realize a three-dimensional ‘topological’ medium for electromagnetic waves  January 9, 2019 An international team of researchers (Singapore, China) constructed the 3-D photonic topological insulator out of a stack of thin plastic sheets embedded with metal antennas acting as tiny electromagnetic resonators. The key breakthrough was made when they realized how to tailor the resonators to interact with electromagnetic waves in a very specific way, granting the waves the desired topological characteristics. The current 3-D photonic topological insulator is limited to electromagnetic waves, at relatively low frequencies. According to the researchers if it can be scaled to optical frequencies there could be applications for creating optical computer chips, […]

Breaking down band structures

Nanowerk  August 22, 2018 A systematic study of symmetry and topology in magnetic materials has been challenging given that there are 1651 magnetic space groups (MSGs). By using an efficient representation of allowed band structures, an international team of researchers (Japan, USA – Harvard University) obtained a systematic description of several basic properties of free electrons in all MSGs in three dimensions, as well as in the 528 magnetic layer groups relevant to two-dimensional magnetic materials. They computed constraints on electron fillings and band connectivity compatible with insulating behavior. Crystalline insulators and topological semimetals could be exploited to use the […]