Round 1: Tossup 13

Interactions are turned on adiabatically in a model of this material that “renormalizes” effective mass and describes how the Fermi surface is distorted. Feynman’s 1955 paper on the “Application of Quantum Mechanics to” this material used Onsager’s model of a 2D system of point vortices. Lee, Osheroff, and Richardson found that a fermionic type of this material has distinct A and B phases when isentropically compressing it in a device named for Isaak (*) Pomeranchuk. Maxons and rotons are quasiparticle excitations in this substance introduced by Landau, whose two-fluid (-5[1])model describes a type of this material that exhibits second sound below the lambda point and becomes a superfluid. (-5[1])For 10 points, name this extremely cold material made of the “3” or “4” isotopes of a noble gas. ■END■ (0[1])

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