Quantum materials appear

  The new state of matter is
  one of the mainstream view is that the name “Bi” of German origin, that white matter, after the 15th century miners repeated the baseless assertion; another often-mentioned argument believes it comes from the Latin alphabet Arabic, meaning “Like antimony.” In any case, it is currently widely recognized that its current English name follows the Latin name proposed after its identification in 1530. However, some people believe that Paracelsus, the father of toxicology, named it in 1526. In short, the true origin of the name “bismuth” has been lost in the long river of history.
  Previously, it was found that bismuth is brittle and fragile, has extremely poor electrical conductivity, and is slightly toxic, so it is not prominent in the world of fiercely competitive materials, let alone comparable to the leaders in high-tech industries such as copper, silicon or lithium. . Bismuth can be used to treat gastroenteritis as antacids, cosmetics, solders, lubricants, pigments, alloys, and can even be found in semiconductors. In short, it is not a particularly high-end application field… However, in terms of basic research, the mysterious element of the name has a unique charm. The reason why bismuth has been studied is that it has significant quantum properties in a strong magnetic field, which will surely promote a new round of revolution in materials science. Bismuth may be one of the strangest and most underestimated elements in the periodic table. It should be an insulator, but it has a certain degree of conductivity. Scientists consider its nucleus to be stable, but in fact it has extremely weak radioactivity. When researchers regarded it as a normal conductor, it showed some superconducting properties.
  Today, bismuth also exhibits unprecedented topological properties. Topology is the branch of mathematics that studies geometric deformation. The idea of ​​using topology to study materials was born in 1960. However, the concept of topological insulators can only be traced back to 2000. The first topological insulators were not manufactured in the laboratory until 2008. Come out: The compound contains antimony and bismuth. As early as 2012, when scientists first began to study bismuth, they had no idea that it had such properties. It is now proved that the long-discovered bismuth crystal is the “chief representative” of a new material category-the second-order topological insulator. The term “topological insulator” has been frequently talked about by materials physicists in the past ten years, and has even attracted the attention of the Nobel Prize Committee. In 2016, the Nobel Prize in Physics was awarded to three researchers in related fields. Because scientific inventions about topological state of matter have set off many revolutions in the industry, such as silicon electronic products in the 1960s, composite materials in the 1980s, and superconductors in the 1990s. There are not many intuitive and concise statements about the new electronic state of matter. In fact, this field studies quantum content such as “spin-orbit coupling” and “energy band inversion”. In order to avoid getting lost in the quantum maze, only the macroscopic properties of bismuth are described below.
  Able to “escape” electronic
  we know, topological insulator is crystalline, such as silicon, diamond, or as salts, their atoms are repeatedly arranged in a manner to follow, this ordered structure gives special crystal physical properties. For example, copper can be used as a conductor. Its atoms can release their own electrons in the connection of the crystal structure to form a so-called “free electron gas”. It is the movement of free electrons that guarantees conductivity. Until the discovery of topological insulators, people have always thought that there are only two types of materials in the world: conductors and insulators. However, the inside of a topological insulator is insulated, but its edges can conduct electricity.
  Internal insulation, surface conduction-this sounds very simple difference, but it makes topological insulators and ordinary insulators have a qualitative difference, because the unique current on the surface is also completely different from the current inside conductors such as metal copper. The interaction between the static atoms and free electrons inside the topological insulator allows the electrons to cross the “obstacle.” Normally, there are lattice defects such as disordered regions, extra atoms, heteroatoms, etc. inside the crystal. In a topological insulator, if electrons encounter lattice defects during their movement, they will not be deflected or diffused as in ordinary conductors, but will pass through these lattice defects as if they were “oblivious”… In conventional conductors, free Electrons move in a disorderly manner. The spin of electrons can be in any direction, and electrons will also be deflected when they encounter heteroatoms. However, in topological insulators, the electron spin is perpendicular to the direction of the current, causing the electrons to be driven to the crystal surface-which not only makes the electrons flow more smoothly, but also helps them avoid internal heteroatoms. In bismuth crystals, electrons are driven out at the same time inside and on the surface of the crystal, and eventually gather on the edges of the crystal. Therefore, although in ordinary conductors, electrons rub against atoms in disordered regions to generate heat and dissipate energy, in topological insulators, lattice defects do not hinder the flow of electrons, so current can be conducted at the edge of the crystal with minimal loss. . In other words, the transmission of electric energy will become almost without heat loss, and the heat loss is precisely the reason that hinders the miniaturization of the microprocessor.
  Suddenly disappeared heat loss
  we know that electricity costs of 50% of the Internet is to cool the large-scale computer clusters, imagine: there is no heat loss of the electronic components can bring how much interest? Soon, while related companies set out to manufacture topological insulators, their theoretical research revealed the source of these unique properties: the specific combination of quantum phenomena and relativity related to the properties of crystal atoms. This heavy atom, which can generate a strong electric field locally, is affected by the relativistic effect for electrons moving at one percent of the speed of light. They are like a magnetic field in the same direction as the electrons. As a result, the quantum property of electron spin gives the electron itself a “magnetic needle” whose orientation is always perpendicular to the direction of the current, which is also conducive to the flow of electrons. In the end, the magnetic field created by the static heavy atoms of the crystal regularly runs through the full path of the current, driving free electrons to the edge, and always maintaining the direction of the electron spin is conducive to their movement.
  The coupling between the electron spin and its motion makes the electron flow a dominant direction: when encountering a chaotically arranged area, they will not deflect, reflect or diffuse, because when there are not too many lattice defects, the electrons can only Keep the original direction, unless its spin is changed. The difference of bismuth crystal is that it can force current to flow to the edge of the crystal. In fact, scientists had discovered this phenomenon of bismuth long before the theoretical literature confirmed its possibility. Previously, the known topological insulators are all first-order, and their characteristic is that the current exists in an interface that is one dimension less than the object itself: when the object is three-dimensional, the current flows through all sides of the object; and if it is an almost flat object, The current only flows through the edges.
  A new round of materials revolution
  in the past, research bismuth once shelved, at least so pure bismuth, because in theory, it’s not a first-order topological insulator. Now, scientists have discovered that it is actually a second-order topological insulator, that is, current flows along a path that is two dimensions less than an object. In other words, in a bismuth cube, the current only exists on the edges of the cube.
  In theory, as long as the “circuit board” is etched on this crystal, the current can pass through without heat loss. Of course, this phenomenon is currently only realized in a low-temperature vacuum environment, and requires an extremely delicate process. This current limited to the edge of the second-order topological insulator still obeys the same quantum law as the first-order topological insulator. This is determined by its unique electronic structure: the static atoms in the crystal core seem to drive free electrons to the edge twice in a row, until the latter are concentrated on the edge… And a scientific research team composed of Chinese and American scientists recently The study found that bismuth is actually a first-order topological insulator, but it is limited to a very special crystal surface-which opens up a new concept, namely crystal topology. The field of topological insulators has just begun to sprout, and bismuth has been regarded as one of the most promising materials. What is expected is what will happen next and what role bismuth will play in it. This metal, which was originally inconspicuous in the periodic table of elements, is about to set off a new round of revolution in the field of materials science in the future.

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