Called an emergent inductor, the device has an inductance that is inversely proportional to its area and does not require a coil or a core - characteristics that are highly desirable for practical applications. The findings, say the researchers, could pave the way to microscale, simple-shaped inductors based on emergent electromagnetism.
Emergent electromagnetism refers to electromagnetism in which the generated electric and magnetic fluxes are described by a concept in quantum mechanics called a Berry phase . Physical systems that exhibit emergent electromagnetism include magnetic systems that have non-collinear spin structures, whereby the direction of magnetization varies with the position of the spins.
When electrons flow along such structures, they can become strongly coupled to the local arrangement of spins and acquire a Berry phase. This phase then acts as an effective electromagnetic field, termed an emergent field.
For example, say the researchers, an emergent magnetic field arises when electrons flow through what are known as topological non-collinear spin structures - those with a particular topology that makes them robust against small distortions or perturbations. The generated magnetic field leads to an extra signal in voltage measurements - known as Hall measurements - that is induced by a physical phenomenon called the topological Hall effect. Given the complex nature of such spin structures, this voltage signal offers a convenient way to explore topological magnetic states in a wide range of materials.
By contrast, an emergent electric field arises from the dynamics of non-collinear spin structures. For example, such a field is generated when a magnetic field drives the motion of domain walls - the boundaries between domains that have different magnetization orientations in magnetic materials.
In 2019, it was shown theoretically that an emergent electric field could also be produced by the current-driven dynamics of non-collinear spin structures. More spectacularly, say the researchers, it was predicted that this field would generate an inductance that is proportional to the rate of