Overview
This lecture introduces spin–charge separation, a phenomenon in which an electron's spin, charge, and orbital behavior act as separate particles in certain materials, focusing on its theoretical development, physical implications, and experimental observations.
Spin–Charge Separation Concept
- In some materials, electrons can 'split' into three independent quasiparticles: spinon (carries spin), holon/chargon (carries charge), and orbiton (carries orbital properties).
- Theoretically, each electron is a bound state of these three quasiparticles, but in certain conditions they behave independently.
- Spin–charge separation is a form of fractionalization, where quasiparticles have quantum numbers that are fractions of the original particle.
Historical Development
- Sin-Itiro Tomonaga first proposed an approximate method for one-dimensional quantum systems showing separation in 1950.
- Joaquin Mazdak Luttinger provided an exactly solvable model in 1963 that demonstrated spin–charge separation.
- In 1981, F. Duncan M. Haldane generalized the concept to all one-dimensional metallic systems with the Luttinger liquid theory.
Physical Implications
- Spinons have zero charge and spin ½; chargons have charge –1 and zero spin.
- These quasiparticles cannot be constructed from electrons, holes, phonons, or photons alone.
- Spin–charge separation is considered one of the most unusual manifestations of quasiparticle behavior.
Experimental Evidence
- In 2009, experiments showed electrons confined in small spaces split into spinons and holons due to mutual repulsion.
- Prior experiments at Lawrence Berkeley National Laboratory directly observed spin–charge separation spectral features.
- Similar effects have been studied in ultracold atoms, showing maximal separation in strongly interacting 1D Bose gases.
Key Terms & Definitions
- Spinon — Quasiparticle carrying the spin property of an electron, with zero charge.
- Holon/Chargon — Quasiparticle carrying the electrical charge of an electron, with zero spin.
- Orbiton — Quasiparticle carrying the orbital degree of freedom.
- Quasiparticle — Collective excitation in a material that behaves like a particle.
- Fractionalization — Phenomenon where quasiparticles carry a fraction of the quantum numbers of elementary particles.
- Luttinger Liquid — Model describing interacting particles in one-dimensional conductors.
Action Items / Next Steps
- Review the concept of Luttinger liquid and its relevance to spin–charge separation.
- Read about experimental techniques for observing quasiparticles in one-dimensional systems.