Novel electron spin interactions and spintronics
Many-body physics provides the basis for understanding and describing the emergent behaviours of numerous interacting particles which are often different and more complex than the properties of the individuals – in other words, the whole is more than the sum of the parts. Among the particles studied is the electron. Conventional electronics is based on current carried by movement of charge (the charged electrons) – it has completely ignored the spin of electrons. In conventional circuits, these spins are random. However, the ability to control the spins – for example, to align or polarise them, hence many-body interactions – offers amazing potential for new devices. Spin-orbit interaction (SOI) refers to the relationship between an electron’s spin state and its orbital angular momentum (the momentum associated with its revolution around the nucleus). The phenomenon forms the basis for spintronics, also known as spin-based electronics or magnetoelectronics, which lays the theoretical foundations for quantum devices. European researchers supported by funding of the ‘Spin and many-body interaction phenomena in semiconductor nanostructures’ (Spinmanybodyseminano) project sought to study and solve numerous problems related to SOIs resulting from the combined effect of two types, namely Bychkov-Rashba and Dresselhaus SOIs, in a two-dimensional electron system (2DES). Scientists derived an exact formula for a specific polarisation function, demonstrating singularities (points at which irregular behaviours are exhibited) leading to Friedel oscillations, strange rippling patterns of positive and negative charge distributions around a stationary charge. In addition, they presented an exact solution to the problem of spin edge states and demonstrated new modes tuneable by applied electric and magnetic fields, thus providing an effective tool to control spin motion in spintronic devices. Investigators also predicted a new type of SOI in double-layer semiconductors, namely the spin Hall drag (SHD) associated with spin accumulation across one layer induced by an electric current along the other layer. Continued project efforts are certain to elucidate more novel phenomena related to SOIs with direct applicability to innovative spintronic devices.
