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How do topological insulators change our understanding of materials with "twisted" energy bands?
With the rapid development of materials science, topological insulators (TIs) have attracted increasing attention from the scientific community. The properties of these materials are very different from traditional insulators. The interior acts as an insulator, but the surface conducts electricity, which means that electrons can only move along the surface of the material. This peculiar physical property stems from the so-called "distortion" phenomenon in its energy band structure, which has changed our basic understanding of matter.
Topological insulators have a twisted band structure that creates a solid surface conductive state that makes them distinct from ordinary insulators.
Topological insulators can exist because there is an obvious energy gap between their valence band and conduction band. However, this property does not mean that they can be transformed into each other without restrictions. Only when the energy band structure changes, can this gap be eliminated and enter a regular conductive state. Therefore, the boundaries between topological insulators and ordinary insulators are relatively clear and exist only in phases that can conduct electricity. Whether based on local symmetry perturbations or external influences, these surface conductive states show extremely high stability.
Although the surface state of ordinary insulators can also conduct electricity, only the surface state of topological insulators has this toughness.
In high-dimensional topological insulators, surface states exhibit many wonderful properties. For example, in a three-dimensional topological insulator with time-reversal symmetry, the spin of the surface state is locked with the direction of motion, forming the so-called spin-momentum locking phenomenon. This situation strongly suppresses the "U-shaped" turn in the scattering process and improves the metal conductivity on the surface.
The potential of topological insulators is not limited to electron transport, however. The surface of this type of material can also support Majorana particles. The emergence of these superconducting phenomena has made topological insulators a hot topic for potential applications in quantum computing and spintronics technology.
The "grand screening" effect of topological insulators is the key to the future of quantum computing.
Topological insulators such as Bi2Te3 and their alloys are prominently mentioned precisely because of their potential applications in the thermoelectric effect. These materials are usually composed of heavy elements, which can effectively reduce thermal conductivity and thus improve thermoelectric conversion efficiency. By studying the band waveforms of topological insulators, researchers now understand how to achieve a reduction in the effective mass of electrons in these materials, thereby increasing conductivity at the valley edges.
Prospects on preparation and application of topological insulators
The synthesis technology of topological insulators is becoming increasingly mature, including metal organic chemical vapor deposition (MOCVD), physical vapor deposition (PVD) and molecular beam epitaxy (MBE). In particular, MBE, because it is performed in a high vacuum environment, can effectively reduce sample contamination and has become the main preparation method for high-quality single crystal thin films. What’s more interesting is that the thin film growth of topological insulators mainly relies on van der Waals forces between layers, which makes the design of integrated circuits on different substrates more feasible.
Future research will focus on how to better control the preparation process of these materials and explore their possibilities in a wider range of applications, especially in the fields of superconducting materials and quantum computers.
With a deeper understanding of the properties of topological insulators, can we develop more materials for quantum technology?
