The Two-Component Model and Metallization of Van der Waals Crystals

Abstract

The paper discusses a model of Van der Waals crystals in which band-gap structures do not form. An effect of strong and chaotic electron-electron repulsion, which was excluded from consideration in the traditional approach, is taken into account. A condensate exists as a result of a dynamic equilibrium among atoms acted upon by constant Van der Waals forces and periodically forming and disappearing covalent bonding. One part of atoms is, on the average, in the ground, and the other, in excited state, to form diatomic virtual molecules. Treated in terms of this pseudoclassical model, the interatomic distances, binding energies, volumes, and pressures at which metallization, for instance, of inert gases and hydrogen, sets in is described by simple relations involving only two spectroscopic parameters of atoms (molecules). Applying pressure to a VdW crystals transfers it from the insulator first to a Bose superconductor, and after that, to a Fermi metal. An empirical relation $T_c \sim N^{2/3}$ between the superconductivity transition temperature $T_c$ and the particles concentration $N$ in chalcogens under pressure is considered as an example of such situation.