Liquid helium is the liquid phase of helium, a noble gas that is colorless, odorless, tasteless, non-toxic, and inert. Helium is the second lightest and second most abundant element in the observable universe, after hydrogen. Liquid helium has several unique properties, particularly at very low temperatures. It is primarily known for its extremely low boiling point, which is around -269 degrees Celsius (-452 degrees Fahrenheit), making it one of the coldest substances known.
Helimagnetism is a type of magnetic ordering that occurs in certain materials, characterized by a helical arrangement of magnetic moments (spins) within a spiral structure. In helimagnetic materials, the magnetic spins rotate in a helical fashion as a function of position, leading to a three-dimensional, non-collinear arrangement. This is different from ferromagnetism, where spins are aligned parallel to each other, and antiferromagnetism, where adjacent spins are aligned in opposite directions.
A supersolid is a state of matter that exhibits properties of both solids and superfluids. In a supersolid, the material has a crystalline structure, which is characteristic of solids, but it also exhibits superfluid-like behavior, such as the ability to flow without viscosity. This fascinating phase of matter combines the rigidity of a solid with the frictionless flow of a superfluid, allowing it to display unique and counterintuitive characteristics.
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4 K. Enough for to make "low temperature superconductors" like regular metals superconducting, e.g. the superconducting temperature of aluminum if 1.2 K.
Contrast with liquid nitrogen, which is much cheaper but only goes to 77K.