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How do free electrons in metals form a type of plasma?

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How scientists use lasers to learn about the universe — plasma Learn about the PHELIX (Petawatt High-Energy Laser for Heavy Ion Experiments) laser at the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, Germany. PHELIX is used for plasma and atomic physics research.

In metallic solids, the free electrons responsible for electrical conduction constitute a type of plasma. This occurs because the valence electrons of metal atoms are nonlocalized, meaning they are not bound to any specific atom but are instead free to wander throughout the entire crystal lattice.123

While the positive metal ions remain fixed in position at lattice points, these mobile valence electrons move among them, creating a system of charged particles that exhibits plasma-like behavior. Because the ions are fixed, however, plasma phenomena in metals are more limited than in gaseous plasmas; they are primarily observed through effects such as plasma oscillations and electron cyclotron waves, where the electron component behaves independently of the ion component. This representation of a metal as a container of free-moving electrons is often referred to in physics as the free-electron model of metals.14