A joint research group of Kyoto University, the University of Tokyo, and Tokyo Institute of Technology discovered that the thermal Hall effect of ruthenium chloride, which is a magnetic insulator, has a universal value defined by quantum mechanics, and it has been more than 80 years since the theoretical prediction. After that, we succeeded in demonstrating "Majorana fermion".
The protons and electrons that make up a substance are called fermions, and each has an antiparticle (for example, the antiparticle of an electron is a positron).On the other hand, neutral fermions with the unique property that particles and antiparticles are the same are called Majorana particles, and their existence was predicted in 1937.In recent years, it has been pointed out that Majorana particles may appear in certain superconductors and magnetic materials, and it has been attracting attention in relation to the realization of topological quantum computers (Note).
In the quantum spin liquid state of ruthenium chloride, a magnetic insulator with a honeycomb-like planar structure (a state in which the liquid is maintained at absolute zero and the spin direction does not change), the joint research group heats while changing the magnetic field under a constant temperature. The Hall conductivity (amount representing the bending of the heat flow) was measured with high accuracy.
As a result, it was found that the thermal hole conductivity is constant at a value that is exactly half of the universal value (quantization value) defined by quantum mechanics regardless of the magnetic field or temperature in a certain range of magnetic fields.Such a phenomenon is called the "quantum Hall effect", and since it was found in an insulator that does not allow electricity to flow this time, it is a quantum Hall effect derived from uncharged particles, and such particles are Majorana particles. It was confirmed that.
This time, definitive evidence of the existence of Majorana fermions has been obtained, and it has also been found that the quantization phenomenon is realized at a high temperature (about 5 Kelvin).By developing a control method for Majorana particles, it is expected to be applied to topological quantum computers that can operate even at high temperatures.
Note) The property that is maintained even if it is continuously deformed is called topology, and it is a stable quantum computer that protects quantum information by using this property.
Paper information:[Nature] Majorana quantization and half-integer thermal quantum Hall effect in a Kitaev spin liquid
