An international team of physicists led by scientists from Yale University in the United States has presented the most convincing evidence to date of the existence of a new type of superconducting material. Confirmation of the existence of a nematic phase of matter is a scientific breakthrough that could open the way to creating superconductivity in a new way.
Phase diagram of FeSe1−xSx, crystal and electronic structure of the superconducting compound FeSe0.81S0.19 / Source: Nature Physics
The theory of superconductivity includes a section that describes how the flow of electric current without resistance can be explained by electronic nematicity, or a phase state of matter in which particles break their rotational symmetry. In theory, chemical compounds can ensure the existence of a nematic phase. This is due to the fact that at room temperature for an electron in atoms, the horizontal and vertical directions of potential motion are not distinguishable in properties. At significantly lower temperatures, electrons can pass into the nematic phase, in which one of the directions becomes more preferable for particles. In some cases, electrons oscillate, favoring one direction or another. This behavior of electrons is called nematic fluctuations.
For many years, physicists could not prove the existence of superconductivity arising due to nematic fluctuations. Now scientists have been able to experimentally confirm the existence of the required phase of the substance in a mixture of iron and sulfur selenides. “These are ideal materials for our study because they exhibit nematic order and superconductivity without magnetism, which makes them difficult to study,” said study leader Eduardo H. Da Silva Neto.
During the experiment, the researchers cooled samples of the material to temperatures below 500 millikelvin. In this state, all movements and vibrations of atoms practically cease. To observe the samples, a scanning tunneling microscope (STM) was used, which can be used to obtain images of the quantum states of electrons. The scientists focused on studying samples that had more pronounced nematic fluctuations. They needed to discover the “energy gap,” which is an indicator of the presence and strength of superconductivity. The experiment proved the existence of the desired discontinuity, which was fully consistent with the theoretical parameters of superconductivity caused by electronic nematicity.
«Proving the existence of the gap has been very difficult because accurately measuring the gap requires complex STM measurements at very low temperatures. The next step is to study this process even more closely. What happens to superconductivity as the sulfur content increases? Will she disappear? Will spin fluctuations return?” Da Silva said about his future plans.
In the future, scientists will not be able to focus on the magnetic parameters of superconductivity, as they did before. One promising direction for future research will be the control of nematic fluctuations. This could potentially lead to the creation of superconductors that can operate at higher temperatures.