helium II

helium-ii的词性：
n.（名词）

1. Liquid helium existing as a superfluid below the transition point of approximately 2.2⁼K at 1 atmosphere and having extremely low viscosity and extremely high thermal conductivity.
（低温物理学用语）氦II：液体氦，转变点之下以超流体形式存在，1个大气压下转变点为约2.2⁼K，具有极低的粘稠度，但有极高的热传导性