" For 10 points, name this property exhibited by certain Helium isotopes that occurs when all viscosity vanishes.
Laszlo Tisza proposed a model to explain the first instance of this phenomenon. One material that exhibits this property has a curiously negative-sloping liquid-solid line on a phase diagram, and therefore can undergo Pomeranchuk cooling. Substances with this property can produce a Rollin film, and one model to explain this property posits an excitation that forms a roton. Quantum soundwaves remove internal resistance to movement in a model of this property postulated by Lev Landau, who proposed that it takes place below the "lambda point." For 10 points, name this property exhibited by certain Helium isotopes that occurs when all viscosity vanishes.
Laszlo Tisza proposed a model to explain the first instance of this phenomenon.
superfluidity [accept word forms]