text: Lee and Osheroff investigated a solid phase of this element using a Pomeranchuk cell.
full_question: Lee and Osheroff investigated a solid phase of this element using a Pomeranchuk cell. This element isthe most common one used to study quantized vortices. New properties of this element were discoveredby Kapitza, Allen, and Misener, all working independently. Two isotopes of this element are continuouslymixed and undergo a spontaneous phase separation in a dilution refrigerator. An isotope of this elementthat is a (*) boson was used by Kamerlingh-Onnes for his most famous discovery. This element is the only one tonever form a solid and standard pressure. Below its lambda point, a form of this element becomes a superfluid,which has zero viscosity. For 10 points, name this element with atomic number two.
first_sentence: Lee and Osheroff investigated a solid phase of this element using a Pomeranchuk cell.
raw_answer:  superfluid 4-helium [or superfluid 4-He; or "3" in place of "4"]