Fig. 2: TATP in CsCl.
a CsCl lattice structure. b Phonon spectrum (ωk) of CsCl along the high-symmetry lines obtained by first-principles calculations. Acoustic phonons at Γ carry \({\mathfrak{q}}=(1,2)\). \({\mathfrak{q}}\) cannot be defined for the triple degeneracy at the R point, because lower two bands cannot be fully separated from the highest energy band owing to the degeneracy between upper two bands along the RM direction. c Wilson loop spectrum of the two lowest acoustic phonons near the Γ point.
