A step into the physics of the future. An experiment has shown that the supersolid, a new form of matter discovered in 2018 combining the features of a solid with those of a superfluid, can rotate without inertia. Authoring the research is a team of the National Institute of Optics of the National Research Council in Pisa (CNR-INO), the European Laboratory of Nonlinear Spectroscopy (Lens) in Florence and the Department of Physics and Astronomy of the University of Florence, which published the study in Science (“Evidence of superfluidity in a dipolar supersolid from nonclassical rotational inertia” DOI: 10.1126/science.aba4309).
Two years ago, the same team had shown that a superfluid gas at very low temperatures – the so-called Bose-Einstein condensate – can develop a solid structure if the atoms in the gas are strongly magnetic, realizing the long-sought supersolid. The atoms act as powerful magnets, interacting with each other so as to form a periodic structure. However, they are not localized but can move freely through the system, as in a superfluid. In this new research, the researchers have verified a 50 years-old theory by the Nobel laureate A.J. Leggett, who had hypothesized the existence of the supersolid and argued that the new state of matter should have an inertia intermediate between those of superfluids and normal solids.
“In order to rotate a normal material (solid, liquid or gas), one must apply to it a certain force, to give it a certain speed which is quantified through the so-called moment of inertia," explains Luca Tanzi of Lens and CNR-INO. "It is known that superfluids, such as liquid helium, rotate without inertia because their particles are delocalized along the whole system, so intuitively the motion of the individual particles cannot be followed. But what would happen to the supersolid, dual-nature state?”
The researchers used a technique similar to the helium torsion pendulum, with the gas rotating back and forth as if it were attached to a spring. From the oscillation frequency, it can be inferred whether the inertia is large, as in a solid, or very small, as in a superfluid. “We have discovered that the oscillation frequency is small, which implies that the inertia of the supersolid is also small, almost equal to that of standard superfluids, although the supersolid has a very clear solid structure,” says Carlo Gabbanini of CNR-INO.
Giovanni Modugno, professor of physics of matter at the Department of Physics and Astronomy of the University of Florence and coordinator of research goes on to comment “This observation demonstrates the co-existence in the supersolid of both superfluidity and a solid structure, a conceptual turning point in the physics of matter. Although the supersolid is small and exists in extreme conditions of temperature and pressure, and as such it cannot be taken out of the laboratory without destroying it, it is a very important test ground for ideas on innovative materials. The phenomena that we are experiencing in the supersolid have a very strong analogy with superconductors. The hope is that one day, having understood all the basic properties of the supersolid, it will be possible to design them on other types of superfluids and superconductors that can live even outside the laboratory.”
