spinful

Spinful is a term used in physics to describe particles or systems that possess intrinsic angular momentum, or spin. Spin is a quantum property that exists independently of any orbital motion and is characterized by a spin quantum number s, which can take values such as 0, 1/2, 1, and so on. For a given s, there are 2s+1 possible spin projections, commonly referred to as spin states. A spinful particle therefore has multiple internal degrees of freedom associated with its spin, whereas a spinless particle has only a single internal state for a given momentum.

In condensed matter and ultracold atomic physics, the term spinful is used to describe models and experiments that explicitly include the spin degree of freedom. For example, spinful fermions such as electrons carry two spin states (up and down) and lead to magnetic phenomena and spin-dependent transport. Spinful bosons include certain atoms with multiple hyperfine states that can behave as spin-1 or higher; systems are described by multi-component order parameters or spinor fields. Theoretical models often label states by spin, leading to spinful versions of the Hubbard model, Heisenberg model, or superconducting pairing with spin structure.

In experiments, spin states can be manipulated with magnetic fields and optical techniques, and spin-orbit coupling links spin to the particle's motion. Spinful systems exhibit phenomena such as spin polarization, magnetism, spin waves, and spin currents, and spin degrees of freedom can be essential for quantum simulation and information processing. By contrast, spinless variants remove the internal spin structure, simplifying theoretical treatment but omitting spin-related effects.