Many solids, but by no means all, are
crystalline. Any molecular bond other than the Van der Waals
bond can under the right conditions easily form a solid. There
is one bond, the metallic bond, that is seen ONLY in
solids.
All interactions between adjacent atoms,
whatever the nature of the “bond,” look like this. The
main mode of quantum excitation of atoms in a solid is
vibrational, as you can guess from what the potential looks
like. When quantum field theory is applied to solids,
collective vibrational modes are found, which physicists call
“phonons.”
In semiconductors, the band gap is
typically from 0.5 to 2.5 eV.
Light-emitting Diodes!
Type 1 Superconductivity!
When physicists refer to “oscillations”
in quantum physics, they generally refer to a system that
can be in either of two states at very slightly different
energies. If the system is started in one of the states, it
will slowly switch over to the other state, and then switch
back. At any given time it is in a superposition of the two
states.
