For many years, physicists have proposed the existence of the axion as a particle. It has drawn interest recently because of its alleged connection to dark matter. However, there is still debate about their very existence.
According to Russian and French experts, the experimental method used to show that an axionic activity exists in particular materials may not have been discovered it as previously thought.
The international team reported their findings in Applied Physics Letters by AIP Publishing, but they were unable to observe the anticipated rise in magnetoconductivity in the charge density wave of the tantalum, selenium, and iodine complex (TaSe4)2I.
The discoveries came three years after a Nature publication that used a related methodology and seemed to offer enough support for an axionic activity.
“A null result, as we report, is in its own an interesting result,” said co-author Pierre Monceau. “The nonreproducibility in the results could be the source of a controversy but, more importantly, may open a scientific debate to uncover experimental ways for investigating this new field.”
In the 1970s, the idea of an axion was put out in particle physics to explain why the strong nuclear force does not display parity violation. A neutron would have developed an electric dipole moment as a result of such a violation, which has not yet been observed experimentally.
A null result, as we report, is in its own an interesting result. The nonreproducibility in the results could be the source of a controversy but, more importantly, may open a scientific debate to uncover experimental ways for investigating this new field.
Pierre Monceau
The precise manner it couples to its electromagnetic field provides evidence for the existence of the axion. Recently, it was proposed that Weyl semimetals, a model for the condensed matter that includes (TaSe4)2I, undergo a similar coupling involving electrons.
Under the right conditions, these electron interactions can induce a charge density wave.
If electrons with spiral motion mirror one another in a magnetic field, charge density waves can acquire axionic properties. The main observation that would support this is a rise in the magnetoconductivity of a wave.
Because of the way its structure is designed, (TaSe4)2I can differentiate electron states based on how helix-like they are.
“Our surprise was to detect no effect in the conductance in a magnetic field,” Monceau said. “We think that, given the lack of further evidence, it is premature to assert that (TaSe4)2I harbors an axionic charge density wave.”
According to Monceau, experiments like monitoring the nonlinear dynamics in a magnetic field along the charge density wave may show axionic properties in charge density wave excitations.
The team plans to carry out more of similar tests in the hopes that the findings would encourage others to create fresh methods for establishing the existence of axion counterparts in condensed matter.
