Are Weyl’s fermions really massless?

The mass behavior of electrons within a solid has a significant impact on the electronic and thermal energy flow. Fail metalloids have emerged as a fascinating class of materials with unique properties. The physical and chemical properties of Weyl metalloids are governed by Weyl fermions, which behave in interesting and unusual ways.

Unlike traditional fermions such as electrons, Weyl fermions are massless particles that behave as an analog of the famous Weyl equation first proposed by Hermann Weyl in the late 1920s. These massless Weyl fermions exist in pairs, with opposing hands. One-handedness of Weyl fermions is related to their topological nature, which leads to a host of fascinating consequences, such as non-trivial surface states and exotic transfer phenomena, which are robust against chaos and disorder.

Massless Weyl fermions have attracted the attention of scientists and technologists because they could be crucial to upcoming advanced technologies. In the realm of quantum technologies, massless Weyl fermions in Weyl metals are potential game-changers due to their ability to enable frictionless quantum information transfer. This can be really useful for future technologies that require accurate and efficient exchange of information.

New research published in physical review b Developed by scientists from the Max Born Institute in Berlin, Germany, and the Indian Institute of Technology in Bombay, India challenged the idea that these Weyl fermions are truly massless.

In particular, if the mass of the Weyl fermions really were zero, then the electron currents generated in the same Weyl node by laser fields with opposite directions, that is, rotating clockwise and counterclockwise, would observe perfect mirror symmetry – just like the light itself . However, these results reveal an unexpected and fascinating deviation from this perfect mirror symmetry, even when the wavelength of the laser field is tuned to transition energies very close to the Weyl point.

The observation remains unchanged even for the weakest light intensities studied. The origin of this effect lies in seemingly small but nonetheless large deviations of Weyl’s mass fermions from zero, even so close to the exact location of Weyl’s nodes: the region of zero mass appears to shrink to a single point.