Quantum phase transitions are fundamental changes in the ground state of a physical system that occur at absolute zero temperature (0 K). Unlike classical phase transitions (like melting or boiling) driven by thermal energy, quantum phase transitions are driven by quantum fluctuations arising from Heisenberg’s uncertainty principle.
Key Features:
- Control Parameter: The transition is triggered by varying a non-thermal parameter such as pressure, magnetic field, or chemical composition.
- Quantum Critical Point: The exact point at which the transition occurs, separating different quantum phases (e.g., from a paramagnet to an antiferromagnet).
- Quantum Fluctuations: Even at 0 K, uncertainty in energy and position allows fluctuations, which can destabilize one phase and favor another.
Examples:
- Superconductor–insulator transition in thin films.
- Magnetic order–disorder transitions in spin systems.
- Mott insulator to metal transition in correlated electron materials.
Importance:
- Near the quantum critical point, even small thermal energies can have significant effects, influencing behavior at finite temperatures (quantum criticality).
- Quantum phase transitions help understand non-classical states of matter, such as topological phases and high-temperature superconductivity.
These transitions reveal how quantum mechanics governs the behavior of matter in extreme conditions and are a major focus in condensed matter physics.