Low-temperature orientational glass transition in molecular ${\mathrm{C}}_{60}$

We propose a model for the description of the low-temperature orientational glass transition in solid molecular ${\mathrm{C}}_{60}$ using the basic concepts and methods of spin-glass and multipole-glass theory. The physical origin of the frustration and the disorder is discussed. We obtain coexistence of orientational and glass orders in the glass phase and a broad maximum of the orientational specific heat in agreement with experimental data. The orientational ordering under pressure is discussed.

Figure 1

(Color online) Order parameters and the heat capacity evolution with the temperature. Here, $d∕c=-0.914$, red solid curve is the heat capacity, dotted blue and dashed green curves are the order parameters $m$ and $\sqrt{q}$, respectively, and the black dashed-dotted curve is the replicon mode ${\lambda }_{\mathrm{repl}}$. The replica symmetry breaking occurs at the temperature $T_0$ corresponding to ${\lambda }_{\mathrm{repl}}=0$; the glass transition temperature $T_g$ is usually very close to $T_0$.

Figure 2

The ratio of the number of molecules with pentagons facing neighbor double bonds, ${\rho }_P$, and the bifurcation temperature $T_b$ as the functions of pressure.