Quantum Physics by Alastair Rae

Author:Alastair Rae
Language: eng
Format: mobi, epub
Publisher: Oneworld Publications
Published: 2011-04-21T20:00:00+00:00

Summary

This chapter has explained how the principles of quantum physics underlie the electrical properties of solids – in particular why some solids are metals that conduct electricity, whereas others are insulators that obstruct the flow of electric current. The main points made are:

• In a solid, the electron waves span the whole sample to form a large number of very closely spaced energy levels, each of which can contain up to four electrons.

• In the absence of a net electric current, equal numbers of electrons move in opposite directions, but this balance is upset when an electric field is applied, provided there are accessible empty states available to the electrons near the Fermi energy.

• Many solids, particularly metals, are formed from crystals where the atoms form a regular, repeating pattern.

• The electrons are significantly affected by the array of ions only if their repeat distance matches the wavelength of the electron wave, in which case a gap appears in the spectrum of energy levels.

• In metals, there are only enough electrons to half-fill the band of states below the gap, which means that there are accessible empty states and hence current can flow.

• In insulators, the band is filled right up to the gap, so there are no accessible empty states and current flow is impossible.

• Our one-dimensional model predicts that solids with an odd or even number of electrons per atom will be metals and insulators respectively. There are exceptions to this rule in the real three-dimensional world.

• The flow of electrons through a metal is obstructed by collisions with thermal excitations and impurities, leading to electrical resistance and Ohm’s law.

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