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 (-5[1])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 model describes a type of this material that exhibits second sound below the lambda point and becomes a superfluid. For 10 points, name this extremely cold material made of the “3” or “4” isotopes of a noble gas. ■END■ (10[1]0[1])

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