spinmomentum

Spinmomentum is a term used to describe the interplay between a particle’s spin angular momentum and its linear momentum, arising from spin-orbit coupling in quantum systems. It is not a separate fundamental quantity but a qualitative description of how spin and motion become correlated in certain materials and structures.

In many-electron systems with strong spin-orbit interaction, eigenstates exhibit spin-momentum locking, where the spin orientation is tied to the momentum direction. Theoretical descriptions use coupling terms such as H_SO ~ λ (S × p)·n or, in condensed matter form, the Rashba Hamiltonian H_R = α (σ × k)·z, which links spin to in-plane momentum. The observable associated with spinmomentum is the expectation value of spin as a function of momentum, often forming chiral or helical textures.

Realizations include the surface states of three-dimensional topological insulators, Rashba-split two-dimensional electron gases, and certain heavy-element semiconductors. These systems can support spin-polarized currents where charge flow implies a preferred spin orientation.

Experimental probes include spin-resolved angle-resolved photoemission spectroscopy, spin-polarized scanning tunneling microscopy, and magneto-transport measurements that reveal spin-dependent conduction and nontrivial Berry phases.

The term spinmomentum is not universally established as a formal quantity in mainstream physics; it is often used informally to describe the coupling between spin and motion. It is closely related to the broader concept of spin-orbit interaction and spin-momentum locking.

Potential applications lie in spintronics and quantum information, where control of spin via momentum, or momentum via spin, enables low-power devices, spin filters, and robust spin qubits.