Supersolids are solid materials such as crystals, which display superfluid properties like those of liquid helium-4. These would include a frictionless flow of molecules in the solid. Since the 1970's scientists struggled to find a supersolid, though not through want of trying. However in 2004 physicists at Pennsylvania University, Moses Chan and Eun-Seong Kim claim to have found supersolid properties in helium-4 which they super cooled to temperatures approaching absolute zero. They used a piece of equipment called a torsional oscillator (Fig. 4) to 'shake' the solid and see how it reacted. Below 175 milliKelvin they believe the material entered a supersolid state where the particles are continually flowing, without friction, but because they are all in the same quantum state they remain a solid. In order to prove this was the case Chan repeated the experiment with helium-3, which is not a boson, and as expected no supersolidity was found.
However, views as to whether this is true are conflicting. Other physicists writing in Nature have argued that when repeating the same experiment they did obtain similar results, but not all the time. There are also conflicting views on what would cause the supersolidity. Some groups found that heating and cooling the solid to remove imperfections removed the supersolidity, which is what would be expected, while others found this was not the case.
Ultimately supersolids are still not fully understood, or even a certainty. However, it seems like only a matter of time before Chan and Kim's work is built on and either supersolids are definitively proven or it is shown that perhaps more research is required.