Physicists have experimentally confirmed the existence of a new type of superconductivity.

In the theory of superconductivity, there is a section that describes how the flow of electric current without resistance can be explained by electronic nematicity—a phase state of matter in which particles break their rotational symmetry.

Chemical compounds that could theoretically support the existence of a nematic phase show that, at room temperature, the horizontal and vertical directions of potential motion for electrons in atoms are indistinguishable in their properties. However, at lower temperatures, electrons can transition into a "nematic" phase, where one direction becomes preferred for the particles. Occasionally, electrons might oscillate, favoring one direction over the other. This phenomenon is referred to as nematic fluctuations.

For decades, physicists have struggled to prove the existence of superconductivity caused by nematic fluctuations, and they have finally confirmed the existence of the required phase of matter in a mixture of iron selenide and sulfur.

“These are ideal materials for our study because they exhibit nematic order and superconductivity without the magnetism that complicates their investigation,” noted Eduardo H. da Silva Neto, the project leader.

The scientists cooled the experimental samples to temperatures below 500 millikelvins. Under these conditions, all atomic movements and vibrations nearly cease. To observe the material, the authors of the article used a scanning tunneling microscope (STM), which allows for imaging the quantum states of electrons.

The researchers focused on samples with maximum nematic fluctuations to detect the "energy gap"—an indicator of the presence and strength of superconductivity. The results of the experiment demonstrated the existence of the required gap, which precisely matched the theoretical parameters of superconductivity induced by electronic nematicity.

“Proving the existence of the gap was very challenging because precise measurements require complex STM techniques at extremely low temperatures. The next step is to study this process even more closely. What will happen to superconductivity as the sulfur content increases? Will it disappear? Will spin fluctuations return?” da Silva Neto outlined the prospects.

Now, scientists can shift their focus away from the magnetic parameters of superconductivity, as was previously customary. One direction for future research is the control of nematic fluctuations, which could potentially lead to the development of superconductors that operate at higher temperatures.

The results of the experiments have been published in the journal Nature Physics.