elektronspin

Elektronenspin, also known as electron spin, is an intrinsic form of angular momentum carried by electrons, a quantum property that does not correspond to the electron’s literal rotation in space but to its quantum state. It is one of the fundamental degrees of freedom in quantum mechanics and plays a central role in magnetic interactions and spectroscopy.

In quantum terms, the electron has spin quantum number s = 1/2, yielding two possible spin projections along any chosen axis: m_s = +1/2 (spin-up) and m_s = -1/2 (spin-down). The spin state is described by a two-component spinor and is governed by the spin operator S, with components related to the Pauli matrices. Measurements of spin along a direction give discrete results of ±ħ/2. The Stern-Gerlach experiment demonstrated this quantization.

The electron also carries a magnetic moment associated with its spin, μ_s = -g_s μ_B Ŝ/ħ, where μ_B is the Bohr magneton and g_s ≈ 2.0023. This magnetic moment interacts with external magnetic fields, producing effects such as Zeeman splitting and contributing to spin–orbit coupling in atoms. Spin-orbit interaction mixes spin and orbital angular momentum and helps determine fine structure and g-factors in spectra.

Electron spin is a fermionic degree of freedom, and the Pauli exclusion principle requires the total wavefunction of identical electrons to be antisymmetric under exchange. This intrinsic property underpins the electronic structure of atoms, chemistry, and magnetism. In applied physics, electron spin is exploited in ESR/EPR spectroscopy, magnetic storage, and spintronics, and serves as a resource in quantum information as a basis for spin qubits.