What does the term "band" refer to in solid-state physics?

In solid-state physics, the term "band" refers to a near continuous array of energy levels that electrons can occupy in a solid. This arises from the overlap of atomic orbitals as atoms come together to form a solid, which leads to the formation of energy bands rather than discrete energy levels.

In a solid, as the number of atoms increases, the energy levels of individual atoms spread out to form bands due to the interactions between atoms. These bands are crucial for understanding electrical, thermal, and optical properties of materials. For example, the valence band is filled with electrons, while the conduction band can accommodate electrons that are free to move, which is essential for electrical conductivity.

The other options do not accurately capture this concept. A finite set of energy levels suggests distinct, non-continuous energy states, which does not align with the behavior of electrons in solids. A specific energy level of an electron implies a singular, isolated energy state, contrary to the band structure. Lastly, the highest energy level in a conductor refers specifically to the top of the conduction band without encompassing the broader range of energy levels that define the band itself. Thus, the most accurate definition in the context of solid-state physics is that "band" refers to a