In order to study the bizarre and exotic matter, scientists have raised the "one-dimensional" to the "two-dimensional"

It is both solid and flows without resistance.

Supersolid imagination. It has both solid and superfluid properties. IQOQI Innsbruck / Harald Ritsch

Recently, Austrian physicists used lasers and ultra-cold gases for the first time to upgrade a strange substance subject with only one dimension to two dimensions, and made great progress in the process of deciphering the mysterious properties of strange matter states.

Supersolids are characterized by both solid and resistance-free fluids, with atoms arranged in uniform and repetitive crystal structures, but at the same time they can flow without losing kinetic energy. This form of matter is extremely strange and ostensibly violates many known laws of physics, but physicists have long been firmly predicting their existence theoretically. Astrophysicists believe that such supersolids may exist inside neutron stars.

Extending one-dimensional supersolids to two-dimensional can help scientists understand how supersolids behave in two-dimensional states. Theoretically, some exotic supersolid features appear only in two dimensions.

To create the supersolid, the researchers suspended a cloud of dysprosium-164 atoms in a light clamp and then used laser cooling techniques to cool the atoms to near absolute zero. Lasers hitting gases usually heat up the gas, but if these laser photons can hit the gas particles from the opposite direction, the particles' motion slows down.

The larger the amplitude of motion of the particles, the higher the temperature, so in this way, researchers can obtain ultracold atoms. After cooling the dysprosium atoms to the lowest possible temperature, the researchers "loosened" the light clamps and let go of the atoms that still carried more energy. These atoms, which are close to absolute zero, are converted into bizarre "Bose-Einstein condensates" in the process.

Once approaching absolute zero, all atoms in the gas lose energy and remain in the same state of energy. If we were to identify some atoms in a cloud of gas, we could only distinguish them according to their energy level. So if the energy states of all atoms are consistent, from the point of view of quantum mechanics, it is equivalent to the gas becoming a whole.

And once matter is in such a state, a door to a strange quantum effect is opened. Heisenberg's uncertainty theorem in quantum mechanics holds that we cannot obtain a definite value for the position and motion parameters of a particle at the same time. But atoms in the "Bose-Einstein condensate" no longer move, all their motion parameters are known, and the position of these atoms becomes uncertain, causing them to occupy an area larger than the space between each other.

Atoms in this state will no longer be in a state of "free dispersion", and they will behave like a giant single particle. Certain substances in the "Bose-Einstein condensate" thus have superfluid properties – they flow without resistance (friction). In a way, it can be said that once they start flowing, they can't stop anymore.

The researchers studied dysprosium-164 because the magnetism of dysprosium and holmium is the strongest of the known elements. After dysprosium-164 atoms become superfluids in an ultra-cold state, they condense into droplets and attract them together like magnetic rods. By fine-tuning the balance between long-range magnetic interactions and short-range atomic interactions, researchers can create supersolids in one dimension— a superfluidic droplet pipe that contains atoms that can flow freely. By adjusting the light clamps and maintaining the density of the atoms, the researchers eventually created a wavy, planar structure, a supersolid that exists in two dimensions.

Two-dimensional supersolids can help physicists study all their properties in two-dimensional space, while also bringing us one step closer to three-dimensional supersolids. As research continues to expand, who knows what incredible phenomena we will find in this strange substance in the future?

reference

Two-dimensional supersolidity in a dipolar quantum gas

https://www.nature.com/articles/s41586-021-03725-7