*Scientists at the University of Pennsylvania have used ultracold atoms to solve a long-standing mystery about why solids melt when heated.*
When we heat a solid, the atoms or molecules that make up the material start to move around more and more quickly. This causes the material to expand and become less dense. Eventually, the atoms or molecules will move so quickly that they can break away from their neighbors and the material will melt.
The melting point of a material is the temperature at which it melts. This temperature is different for different materials. For example, ice melts at 0 degrees Celsius, while steel melts at 1,538 degrees Celsius.
The melting point of a material is determined by the strength of the forces that hold the atoms or molecules together. In a solid, these forces are strong enough to keep the atoms or molecules in place, even when they are moving around quickly. However, as the temperature increases, these forces become weaker and weaker. Eventually, the forces are no longer strong enough to hold the atoms or molecules together and the material melts.
The Penn physicists used ultracold atoms to study the melting process in a very simple system. They created a gas, trapped an ultra-cold atom that contains strontium and ytterbium atoms held in place by lasers, and then heated it to watch how it melted.
They found that the melting process takes place in two steps. First, the atoms start to move around more and more quickly, forming small clusters. These clusters then grow larger and larger until they eventually merge together to form a liquid.
The physicists also found that the melting point of the gas was much lower than the melting point of the solid. This is because the atoms in the gas are not as tightly packed as they are in the solid, so they do not need as much energy to break away from their neighbors.
This work provides new insights into the melting process and could help scientists develop new ways to control the melting point of materials. This could have important applications in a variety of fields, such as materials science, engineering, and pharmaceuticals.
