A team of scientists from Tokyo Institute of technology and Yokohama National University announced in the latest issue that they have found a strange mechanism by which spin perturbations pass through a seemingly impassable region of the quantum spin liquid system and recognize the unconventional spin transport in quantum spin liquid. This new cognition will be the next generation of electronic devices Even quantum computers set off another wave.
Why is the discovery of such a strange mechanism a revolutionary new leap forward, which may cause another wave in the next generation of electronic devices and even quantum computers? We have to start with a brief introduction to quantum spin liquids and their basic properties, which many people are unfamiliar with.
quantum spin liquid, abbreviated as QSL, refers to an unusual material phase of matter in condensed matter physics, also known as quantum matter, which can be formed by the interaction of quantum spins in some magnetic materials. Quantum spin liquids are usually characterized by their long-range quantum entanglement, “fractional excitation” and the absence of ordinary “magnetic order”. Fractional excitation, in physics, refers to the phenomenon that quasiparticles of a system cannot be constructed as a combination of its basic components. One of the earliest and most famous examples is the fractional quantum Hall effect, in which the constituent particles are electrons, while the quasiparticles carry some electronic charges.
“magnetic order”, or also known as: magnetic order, in physics, refers to the order of magnetism, “order” or “disorder” indicates whether there is some symmetry or correlation in the magnetic system.
the quantum spin liquid state was first proposed by physicist Phil Anderson in 1973. It is the ground state of the spin system which interacts with its neighbor antiferromagnetically on a triangular lattice. That is, adjacent spins try to align in the opposite direction. When Anderson put forward a theory to describe high temperature superconductivity by disordered spin liquid state in 1987, quantum spin liquid attracted more and more attention.
the simplest magnetic phase is a paramagnetic, in which each spin is independent of the rest, just like atoms in an ideal gas. This highly disordered phase is the general state of the magnet at high temperature, in which thermal wave is dominant. After cooling, the spin usually enters the ferromagnetic stage. At this stage, the interaction between the spins causes them to align into large patterns, such as fields, stripes, or checkerboards. These long-range patterns, called magnetic orders, are similar to regular crystal structures formed by many solids.
quantum spin liquids provide a dramatic alternative to this typical behavior. Compared with the ferromagnetic spin state, a visual description of this state is “liquid” with disordered spin, just as liquid water is in more disordered state than crystalline ice. However, unlike other disordered states, quantum spin liquid keeps its disordered state at a very low temperature. More modern characterization of quantum spin liquids involves their topological ordering, long-range quantum entanglement properties, and the excitation of anyons.
in August 2015, another evidence of quantum spin liquid was observed in two-dimensional materials. A team of researchers from Oak Ridge National Laboratory, Cambridge University, and Max Planck Institute for complex systems physics in Germany measured the first characteristics of these fractional particles called Majorana fermions in two-dimensional materials with graphene like structures. Their experimental results have been successfully matched with a major theoretical model of quantum spin liquids called the Kitaev honeycomb model.
as shown in the above figure, the Kitaev model has a honeycomb lattice with serrated edges, and the red, blue and green lines represent x, y, Z. The vertices of such a cellular network represent sites with two possible spin states. An interesting feature of this model is that the magnetic pulse applied to the left shadow area will cause the spin change in the right shadow area, but not in the middle part. So far, the mechanism of the spin disturbance crossing the intermediate region is not clear.
the electronic devices we know are close to their theoretical limits, which means that new technologies are needed to achieve better performance or higher miniaturization. The problem is that modern electronic technology focuses on manipulating current, so it focuses on the collective charge of moving electrons. But what if signals and data can be encoded and transmitted in a more efficient way?
to this end, scientists have entered a new technology field called spintronics. Spintronics is a compact term for spin transport electronics, so it is also called spin transport electronics accurately. It refers to the study of the intrinsic spin of electrons in solid-state electronic devices and its associated magnetic moment in addition to the basic electronic charge. The difference between spintronics and traditional Magnetoelectronics is that spin is controlled by both magnetic field and electric field.
spintronics is an emerging technology field which is expected to completely change electronic technology, and is expected to become a key participant in the development of quantum computers. In spintronic devices, the most important feature of electrons is the spin of electrons, which can be widely regarded as their angular momentum and the fundamental cause of magnetic phenomena in solids. Many physicists all over the world are trying to find a practical way to generate and transport this “spin packet” through materials.
the above-mentioned quantum spin liquids and their basic properties are introduced. Next, we can briefly understand the research results of this revolutionary new leap forward made by the Japanese research team.
in this recent study of the research team in Japan, the researchers conducted a theoretical analysis on the unique spin transport characteristics of a specific system in the Kitaev model.
this two-dimensional model includes a cellular network in which each vertex carries a rotation. The special feature of Kitaev system is that its behavior is similar to that of quantum spin liquid due to the special interaction between spins. Simply put, it is impossible to arrange spins in a unique and optimal way of “keeping each spin happy” in this system. This phenomenon is called spin depression. Spin frustration, also known as spin frustration, or spin instability, comes from a special phenomenon in condensed matter physics called geometric instability, or geometric depression. This spin depression causes spin to run in a particularly disordered way. An important feature of
Kitaev model is its local symmetry. Such symmetry means that spins are only related to their nearest neighbors and not to distant spins, thus suggesting that spin transport should be hindered. However, in fact, although the small magnetic disturbance on one edge of the Kitaev system does show a change in the spin at the relative edge, even if these disturbances do not seem to cause any change in the magnetization of the symmetric region in the center of the magnetic rod. In their paper, the research team elucidated this interesting mechanism.
the researchers applied a pulsed magnetic field on an edge of the Kitaev quantum spin liquid to trigger the transmission of spin packets, and numerically simulated the real-time dynamics. As shown in the figure below, the magnetic pulse at the left end causes spin excitation due to the time variation of its spin, which will be converted into the motion of the Majorana particle and then transmitted to its relative edge through the material. The results show that the magnetic disturbance crosses the central region of the material through the propagation of the Majorana fermion. These are the exact behavior of the particles, not the real ones.
the quantum spin liquid materials studied in this paper can be used in data recording and storage. In particular, topological quantum computation can be realized by spin liquid state. The development of quantum spin liquid will also help to understand high temperature superconductivity.