Physicists at Japan’s RIKEN Research Institute have found that hypothetical dark matter particles called axions are capable of generating mysterious strings inside topological insulators.
Researchers have studied an unusual phenomenon that occurs inside a topological insulator – a material that is a dielectric (insulator) in volume, but can conduct an electric current on the surface. Typically, when a DC conductor is placed in a magnetic field, a transverse voltage (potential difference) occurs, which is called the Hall effect. However, in topological insulators, an anomalous Hall effect occurs when a voltage is generated in the absence of an external magnetic field.
Scientists have come to the conclusion that in topological insulators, when photons and axions interact, extended filamentous configurations – axion strings can arise, which explains the anomalous Hole effect.
The axions have not yet been discovered. It is believed that these particles can be candidates for the role of dark matter, an invisible mass that affects the motion of cosmic bodies and makes up 80 percent of the matter in the Universe. In addition, they can solve the problem in quantum chromodynamics, which is the violation of CP-invariance. In June 2020, the XENON1T experiment at the Gran Sasso laboratory in Italy reported that they could detect the axion, but this result has yet to be confirmed.
CP-invariance is called the conservation of physical laws during the operation of mirroring the system with the simultaneous replacement of all particles with antiparticles. However, it has been shown that CP invariance is violated in some experiments with weak interaction.