Surprise in the quantum world: Disorder leads to ferromagnetic topological insulator

Nanowerk   March 21, 2023 The recent realizations of the quantum anomalous Hall effect in MnBi2Te4 and MnBi4Te7 benchmark the (MnBi2Te4)(Bi2Te3)n family as a promising hotbed for further quantum anomalous Hall effect improvements. However, the quantum anomalous Hall effect realization is complicated in MnBi2Te4 and MnBi4Te7 due to the substantial antiferromagnetic coupling between the septuple layers. Although ferromagnetic state can be stabilized by interlacing the septuple layers with an increasing number n of Bi2Te3 quintuple layers the mechanisms driving the FM state and the number of necessary quintuple layers are not understood, and the surface magnetism remains obscure. An international team […]

Chip-scale Floquet topological insulators to enhance 5G wireless communications

Phys.org  May 30, 2022 A team of researchers in the US (Columbia University, City University of New York, UT Austin, industry) introduced Floquet topological insulators for radio-waves with a unique design, based on the quasi-electrostatic propagation of radio signals in switched-capacitor networks. In their previous work they developed photonic topological insulators (PTI) chips that could be used to create full-duplex phased-array wireless technology, which combines two different 5G wireless capabilities: full-duplex and multi-antenna operation. PTIs do not allow the propagation of electromagnetic waves in their bulk, but they ensure efficient and robust wave propagation on their boundaries, however shaped. These […]

Is it topological? A new materials database has the answer

MIT News   May 19, 2022 The recently introduced theories of topological quantum chemistry and symmetry-based indicators (SIs) have facilitated the discovery of topological phases of matter and large-scale searches for materials with experimentally accessible topological properties at the Fermi energy (EF). Away from EF, energetically isolated bands and topological gaps are also useful in numerous experimental settings; they can be accessed via (electro)chemical doping, electrostatic gating, hydrostatic pressure, and nonequilibrium photoexcitation and are relevant to Floquet engineering and nonlinear optical experiments. An international team of researchers (Spain, USA – MIT, Princeton University, Germany) has completed a catalog of stable and […]

Quantum one-way street in topological insulator nanowires

Phys.org  May 12, 2022 Recently quantum mechanical non-reciprocal transport effects that enable a highly controllable rectification were discovered. One such effect is magnetochiral anisotropy (MCA) in which the resistance of a material or a device depends on both the direction of the current flow and an applied magnetic field. However, the size of rectification possible due to MCA is usually extremely small because MCA relies on inversion symmetry breaking that leads to the manifestation of spin–orbit coupling, which is a relativistic effect. To overcome this limitation, an international team of researchers (Switzerland, Germany, Belgium) artificially broke the inversion symmetry via […]

Hybrid quantum bit based on topological insulators

Science Daily  April 14, 2022 Topological qubits are considered to be particularly robust and largely immune to external sources of decoherence and appear to enable fast switching times comparable to those achieved by the conventional superconducting qubits used in current quantum processors. However, it is not yet clear whether we will ever succeed in producing topological qubits as a suitable material basis is still lacking to experimentally generate the special quasiparticles required for this without any doubt. An international team of researchers (Germany, UK, Denmark, the Netherlands) implemented superconducting transmon qubits with (Bi0.06Sb0.94)2Te3 topological insulator. According to the team microwave […]

Making a ‘sandwich’ out of magnets and topological insulators, potential for lossless electronics

Nanowerk  April 3, 2022 Inducing magnetic order in topological insulators via proximity to a magnetic material offers a promising pathway towards achieving quantum anomalous Hall (QAH) effect at higher temperatures for lossless transport applications. An international team of researchers (Australia, Singapore, USA – UC Berkeley) demonstrated the growth of a MnBi2Te4 / Bi2Te3 /MnBi2Te4 heterostructure via molecular beam epitaxy and probed the structure’s electronic structure using angle resolved photoelectron spectroscopy. They observed strong hexagonally warped massive Dirac fermions and a bandgap of 75 ± 15 meV. The 2D MnBi2Te4 ferromagnets induced magnetic order in the ultra-thin topological insulator Bi2Te3 via […]

Quantum material to boost terahertz frequencies

Science Daily  October 20, 2021 An international team of researchers (Germany, Spain, Russia) investigated the ultrafast carrier dynamics in topological insulators (TIs) of the bismuth and antimony chalcogenide family, where they isolated the response of Dirac fermions at the surface from the response of bulk carriers by combining photoexcitation with below-bandgap terahertz (THz) photons and TI samples with varying Fermi level, including one sample with the Fermi level located within the bandgap. They identified distinctly faster relaxation of charge carriers in the topologically protected Dirac surface states, compared to bulk carriers and they observed THz harmonic generation without any saturation […]

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 […]