[DigitalToday reporter Jinju Hong (홍진주)] A study on superconductors has found that “virtual photons” that do not actually exist can reduce performance. The research is closer to experimentally verifying a distinct quantum-mechanical phenomenon than being directly linked to developing high-temperature superconductors. The study was introduced in the global science journal Nature.

According to the IT media outlet Ars Technica on Feb. 27 (local time), the research starts from quantum field theory. Vacuum is usually thought of as “space with nothing,” but modern physics does not see it that way. Though invisible, space is filled with unseen energy fields. Photons, or particles of light, are also a form of energy created when those fields slightly fluctuate.

There are 2 kinds of light. One is “real photons” that can be directly observed, such as with lasers. The other is “virtual photons,” which cannot be seen or captured directly but transmit forces between particles. Virtual photons have no tangible existence, but their effects can physically appear. The researchers sought to confirm whether this “invisible light” could affect a superconductor.

The key material is boron nitride. It has a structure in which hexagonal, honeycomb-like layers are stacked, and it has one feature. It responds strongly only to light of a specific wavelength. In other words, it is like a resonant box that rings only at a specific pitch, or frequency. If energy corresponding to that frequency forms nearby, a similar effect can appear even without real light.

The researchers used a superconductor called “kappa-(BEDT-TTF)2Cu[N(CN)2]Br,” or “kappa-ET” for short. This material becomes superconducting only at ultralow temperatures, around 12 kelvin, but it operates somewhat differently from existing superconductors. Scientists have suggested that “carbon-carbon double-bond vibrations” inside the material could be related to superconductivity. But directly manipulating that has not been easy experimentally.

The vibration frequency of that bond was found to almost match the infrared wavelength to which boron nitride responds strongly. That means placing boron nitride nearby changes the virtual-photon environment, creating the possibility that carbon-bond vibrations could be affected. The researchers therefore created a structure in which boron nitride was layered on top of kappa-ET.

The experiment found that when boron nitride was present, the superconductor’s ability to push out magnetic fields weakened. In other words, superconducting performance fell. No such change appeared when other materials were placed on the surface, and similar superconductors were also unaffected. This suggests the interaction between kappa-ET and boron nitride is specific and occurs even without real photons.

The study is unlikely to directly lead to developing high-temperature superconductors. But it is meaningful in showing that superconductivity can be controlled through an electromagnetic environment as well as temperature and pressure. Given that various layered materials can form resonance at different wavelengths, it could develop into a new approach to precisely probe and control phenomena inside superconductors.

In summary, the study is less a superconducting breakthrough than an experimental confirmation that “invisible light can shake real materials.” If such small discoveries accumulate, they could one day offer clues to making superconductors that operate under more realistic conditions, Ars Technica reported.