Charge density waves (CDWs) are periodic modulations of the electronic charge density in a material, typically accompanied by a distortion of the atomic lattice. This phenomenon arises due to interactions between electrons and the crystal lattice, especially in low-dimensional systems like quasi-one-dimensional conductors.
Key Features:
- Periodic Structure: The electron density oscillates with a specific wavelength, forming a wave-like pattern across the material.
- Lattice Distortion: The ionic lattice adjusts to this charge modulation, creating a coupled electron–phonon state.
- Peierls Instability: In one-dimensional conductors, a CDW can open a gap at the Fermi surface, lowering the system’s energy and causing the material to become insulating at low temperatures.
Significance:
- Quantum Coherence: CDWs exhibit quantum coherence and can be pinned or slide under external fields, similar to superconducting currents.
- Competition with Superconductivity: In some materials (like cuprates or transition-metal dichalcogenides), CDWs compete with or coexist with superconductivity.
- Collective Excitations: CDWs support collective modes such as phasons (phase shifts) and amplitudons (amplitude fluctuations).
Charge density waves are a striking example of emergent order in strongly interacting electron systems, with implications for understanding electronic transport, phase transitions, and quantum materials.