The Supersolid State
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Out of all of the elements on the periodic table, helium has some of the most interesting properties. These properties occur in both of helium’s isotopes, but are easiest to see in helium’s most abundant isotope, 4He. One of the things that make helium so unique is that when subjugated to pressure under 25 bars, and temperatures cooler than 2K, it will not freeze into an ordinary solid, even as temperatures get close to 0K. Instead, when the temperature gets below the lambda point (about 2.17K), a phase transition occurs in which the regular liquid helium becomes a superfluid called helium II. This superfluid state was first observed in helium in 1938, independently by Kapitza and then later that year by John Allen and A.D. Misener. Going beyond this, it was thought that this superfluid state might exhibit unusual properties when forced into becoming a solid by increasing the pressure. Thus the search for something called the supersolid began. The author worked alongside Dr. Clement Burns of Western Michigan University and undergraduate Dan Ulrey in trying to find this supersolid state In the end, we concluded that the supersolid state in 4He does not exist in within the temperature range that we tested in.