Particles refer to the smallest component of matter that can exist in a free state, including electrons and neutrons. The cornerstone of modern physics — — The physical standard model is essentially a "family tree" of a particle family, and its members are familiar to everyone. The Higgs boson, which finally revealed its beauty, was sought after by scientists from all walks of life as soon as it came out.
But there is an equally important class of particles that nobody cares about Of course, this is understandable, because these "quasi-particles" do not really exist, but their unique physical properties are enough to change modern science and technology. In a recent report, the British magazine New Scientist listed five quasi-particles that "don’t exist" but can change the face of the world.
Phonon: electric cowboy
In 2012, the Large Hadron Collider (LHC) at CERN discovered the Higgs boson, which is the mass source of other particles. So far, all 62 kinds of elementary particles have been discovered, and the standard model of particle physics has been perfected.
But without phonon, all this would not have happened.
The concept of phonon is developed in the process of studying lattice vibration. Li Baowen, director of the Center for Phononics and Thermal Energy Science of Tongji University, once explained that phonons are not real particles, but quasi-particles, which are quantized lattice vibrations. It is called a phonon because the essence of "sound" is the "vibration" of an object. In fact, the Greek word for phonon means sound.
The name phonon was first put forward by Igor Tamm, a physicist in the former Soviet Union, in 1932. He pointed out that just as light corresponds to electrons, sound waves can be associated with some particles we call "phonons". In solids, especially in semiconductors and insulators, "heat" is conducted through lattice vibration, that is, "phonons" are carriers of heat.
At room temperature, phonons are quasi-particles, and the heat conduction of solid materials is mainly realized by phonons. But at extremely low temperature, these quasi-particles "incarnate" into a group of "cowboys", driving away the "cattle" composed of electrons. These electrons act uniformly, and their resistance is almost zero, which is the principle of low temperature superconductivity.
It is the huge electromagnetic field created by superconducting magnets that makes protons bend in the large circular orbit of LHC. In the magnetic resonance imaging (MRI) scanner, these superconducting magnets "transform" as a command, guiding oxygen atoms in human tissues to "dance" and releasing traceable radio signals. In addition, phonons also play an important role in the field of thermoelectric materials. These thermoelectric materials can convert thermal energy into electrical energy, and it is also expected to realize scientists’ dream of reusing waste heat from automobile engines to supply power for electronic products.
Magneton: the king of spin
Since Tam put forward the concept of "phonon", scientists have gradually found many such quasi-particles in solids. Another such particle originates from spin, a quantum property that is the basis of magnetism. Spin is like an arrow on an atom, pointing south or north; When all spins in matter are aligned, a magnetic field appears. However, when this spin state is constantly reversed, a wave effect is created, which scientists call "magnon".
Ordinary computers and smart phones need electricity to store information, but the information of equipment power failure cannot be obtained. If a magnon is used, the information storage will depend entirely on the magnetic field without electricity, which is called Spintronics. The advantage of this method is that it consumes little power — — Excessive power consumption is one of the main problems encountered in miniaturization of transistor chips. If the magnetic oscillator is controlled by electromagnetic waves, the computer can completely get rid of the shackles of wires and electricity.
Exciton: the secret weapon of plants
The earth gets more energy from the sun in an hour than all mankind consumes in a year. Plants play the role of energy catchers, and excitons are the "secret weapons" for plants to perform this task.
In any substance, electrons exist in different energy levels. When a photon strikes the surface of an object, it will excite electrons to a higher energy level, leaving a hole. Electrons are negatively charged and holes are positively charged. Under certain conditions, the Coulomb attraction between them will bind them together in space, so the complex formed is called excitons.
The leaves of plants contain light-trapping proteins, and the electrons in the light-trapping proteins will be excited to absorb photons and leave their positions, leaving a hole, electrons — Excitons formed by hole pairs will float around the photosynthesis production line of plants.
When excitons arrive at specific positions where they are needed, electrons recombine with holes and release energy, which plants use to decompose water into hydrogen and oxygen.
This photosynthesis is the root of life on earth, and human beings have been looking forward to simulating this reaction in solar cells. In 2013, researchers at the Massachusetts Institute of Technology found a way to "photograph" excitons directly, which took a key step towards the ultimate goal.
According to the online edition of Science magazine in 2009, Leonid Butov, a physics professor at the University of California, San Diego, and his colleagues have made several transistors based on excitons. These transistors are expected to become the basic modules of new computers, and the circuits assembled by them will become the first computing device using excitons in the world.
Mayorana Fermion: Quantum Hero
If you want to have a real multi-process computer, you can turn to a quantum computer for help. The quantum computer, which is still in its infancy, makes use of subtle and uncertain quantum states and can give multiple solutions to the same problem at the same time. As long as the external environment does not disturb the "magic" of the quantum computer, it can run stably.
Majorana quasiparticles can provide "qubits" for quantum operations, which makes quantum computers more powerful.
The information in an ordinary computer is stored in "bits", and each bit is coded as 0 or 1; Information bits in a quantum computer can exist as 0 and 1 at the same time, but this superposition state is very fragile. For this reason, physicists have been looking for ways to make qubits more stable.
In 1930s, Italian theoretical physicist ettore majorana predicted that there must be a particle, which is the same as its antiparticle. The concept of "majorana particle" was born. It has no mass and no charge. It is its own antiparticle and always appears in pairs. Because of its special properties, majorana particles are electrically neutral and rarely interact with the environment, so it becomes an ideal carrier for quantum information coding.
Since majorana particles always appear in pairs, which means that there are two copies of the information they contain, theoretically speaking, majorana qubits are more tolerant to external noise. However, according to Attila Geresdi of QuTech Institute in the Netherlands, these qubits exist in the background of huge electronic effects, and it is very tricky to extract the information of majorana quasiparticles.
In June this year, the research team of Jia Jinfeng of Shanghai Jiaotong University wrote in the Physical Review Express that they had successfully captured the Mayorana fermion in the laboratory through a special artificial film composed of topological insulator materials and superconductor materials, which not only contributed to the development of quantum computers, but also helped to further uncover the mystery of dark matter.
Wilfermion: Double-faced Jiaowa
"Weyl fermions" are like shy "cousins" of electrons. In 1929, the German scientist H. Weyl proposed that there is a kind of electron with no "mass" and can be divided into two different "chirality" of left-handed and right-handed, and this electron is called "Wilfermion".
The fermion has two key characteristics: massless and chiral. The lack of mass means that it can move at high speed, and at the same time, it is extremely resistant to interference that is inconsistent with its chirality, which makes it difficult to scatter: two different types of fermion streams can be close together without interaction. It has been suggested that these properties can make it the basis of computers beyond spintronics computing power.
However, for more than 80 years, scientists have not observed the fermion in the experiment, and the semi-metallic materials with the characteristics of fermion have only recently appeared. On July 16, last year, Science magazine published the experimental results of the team of physicist Zaid Hassan of Princeton University. The team announced that they found "Waier Fermion" in "Waier Semimetal"; On July 20th, official website, Institute of Physics, Chinese Academy of Sciences, announced that the research team led by Fang Zhong, a researcher from the Institute, had successfully discovered the Verfermion in TaAs crystal for the first time. Therefore, the era of "Weyl Weyltronics" has appeared on the horizon, but there is still a long way to go.
