Stuttgart physicists unambiguously prove a supercontest body for the first time
Exotic quantum matter is crystal and superfluid at the same time
Supersolid bodies (in the English supersolids) describe a state of aggregation, which can be described simply as solid and fluid at the same time. The proof of this exotic quantum matter has been fueled by a veritable competition in recent years. A team led by Prof. Tilman Pfau and Tim Langen at the 5. Physical Institute of the University of Stuttgart succeeded for the first time the experimental proof that the long predicted, suprasolide state of matter actually exists. The researchers describe their findings in the journal Nature.
In everyday life we know three states of aggregation of matter - solid, liquid and gaseous. If matter is cooled to an extreme, other states of aggregation such as superfluids arise, in which the atoms can move without resistance and without friction. At the atomic level, quantum mechanics comes into play: Individual particles such as atoms or electrons can overlap and, for example, appear unpredictably and randomly in two different places. Theoretically, however, it is also possible that entire states of aggregation such as solid or liquid are superimposed to form new states of aggregation with new properties. A super solid is such a superposition and consists of the crystalline structure of a solid and a super liquid. A particle could therefore unpredictably and accidentally be part of the crystal or the superfluid.
In this experimental setup, the Stuttgart researchers succeeded in using lasers and magnetic fields to generate the supercardial body from dysprosium atoms. Photo: Wolfram Scheible, University of Stuttgart
The super solid produced at the University of Stuttgart consists of dysprosium atoms that behave like small magnets. In the experiment, the atoms are cooled down to almost absolute zero (-273 ° Celsius). At this point, two types of interaction between the atoms play a role: when two atoms come very close, they collide like billiard balls. At the same time, due to the magnetic interaction, they can also attract or repel each other over longer distances. In order to create a super solid, the researchers balance the relationship between these two forces in such a way that a crystalline lattice structure and so-called superfluidity - a smooth flow of atoms - develop at the same time. “We were able to determine the periodic crystal formation directly optically and test the quantum mechanical superposition by means of interference experiments,” explain Mingyang Guo and Fabian Böttcher, postdoc and doctoral student at the 5th Physics Institute, their measurements.
Proof with the help of sound waves
The final proof that the matter created in the experiment is indeed a supernatant was obtained by studying two types of sound waves traveling through the supernatant at different velocities of sound. Such sound waves are very different in different materials - in the air, for example, the sound is much slower than in water. This "normal" sound is also found in the supercontest body. Because the supernatant solid at the same time and is liquid, but can also observe a characteristic second form of sound waves in which the crystal and the superfluid move exactly opposite each other. This results in sound waves with a very low speed, which the Stuttgart researchers were able to observe for the first time in the experiment.
Observations of a super solid have been reported again and again in recent years. But then it later turned out that no two types of sound were measured. "In this worldwide race we have now succeeded for the first time in demonstrating all three conditions for a suprasolid state in an experiment with ultra-cold dysprosium atoms," says Tilman Pfau happily. For the first time, the experiments by the Stuttgart researchers open up the possibility of investigating the exotic properties of super solids in detail.
Figure a) shows a small crystal, in c) a superfluid was prepared from the atoms, b) shows the superposition of both - the super solid. In a certain parameter range, the two properties, which are mutually exclusive in the classical world, solid and liquid, can exist in a quantum mechanical superposition.
Technical contact:
Prof. Tilman Pfau, University of Stuttgart, 5. Physical Institute, Tel .: + 49 711 685-68025
