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Concept
Electric dipole spin resonance
Summary
Electric dipole spin resonance (EDSR) is a method to control the magnetic moments inside a material using quantum mechanical effects like the spin–orbit interaction. Mainly, EDSR allows to flip the orientation of the magnetic moments through the use of electromagnetic radiation at resonant frequencies. EDSR was first proposed by Emmanuel Rashba.
Computer hardware employs the electron charge in transistors to process information and the electron magnetic moment or spin for magnetic storage devices. The emergent field of spintronics aims in unifying the operations of these subsystems. For achieving this goal, the electron spin should be operated by electric fields. EDSR allows to use the electric component of AC fields to manipulate both charge and spin.
Free electrons possess electric charge and magnetic moment whose absolute value is about one Bohr magneton .
The standard electron spin resonance, also known as electron paramagnetic resonance (EPR), is due to the coupling of electron magnetic moment to the external magnetic field through the Hamiltonian describing its Larmor precession. The magnetic moment is related to electron angular momentum as , where is the g-factor and is the reduced Planck constant. For a free electron in vacuum . As the electron is a spin-1⁄2 particle, the spin operator can take only two values: . So, Larmor interaction has quantized energy levels in a time-independent magnetic field as the energy is equal to . In the same way, under a resonant AC magnetic field at the frequency , results in electron paramagnetic resonance, that is, the signal gets absorbed strongly at this frequency as it produces transitions between spin values.
In atoms, electron orbital and spin dynamics are coupled to the electric field of the protons in the atomic nucleus according to the Dirac equation. An electron moving in a static electric field sees, according to the Lorentz transformations of special relativity, a complementary magnetic field in the electron frame of reference.
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