Dongwook GO
Spintronics is one of the candidates that can achieve the key goals of the next generation information technology; high speed, scalability, and low-energy consumption. The discovery of spin-orbit torque a decade ago revolutionized the field and opened a promising route for electric control of magnetism. This has led to commercial device applications, e.g. spin-orbit torque random access memory. To enhance the efficiency, various novel ideas have been proposed; spin-momentum locking from Rashba states, topological surface states, oxide heterostructures, antiferromagnets, etc. Because these rely on strong spin-orbit interaction to electrically induce nonequilibrium spin density or current, the choice of materials is limited to heavy elements which are scarce on earth and often incompatible with mass production.
Recently, we proposed a fundamentally new direction by using orbital angular momentum (OAM) and its current. The orbital degree of freedom has been barely exploited so far because of the expectation that strong crystal field would suppress a coherent superposition. In spite of quenching of equilibrium orbital angular momentum, we have found that it is possible to electrically induce excitations of OAM and its current in nonequilibrium induced by an external electric field. We have shown that the efficiency of orbital current generation via orbital Hall effect far exceeds that of the spin current generation. Moreover, since the mechanism is independent from spin-orbit interaction, we have a broader choice of materials including light materials. In the last few years, numerous experiments have found evidences of the orbital current, have demonstrated its potential impact on spintronic devices, and have led to the birth of orbitronics in which we aim to build new type of devices by using electronic orbital information. All these developments are the tip of an iceberg and can potentially lead to a new paradigm of quantum transport phenomena. A new perspective from orbitronics may shed light not only on spintronics but also other important areas of condensed matter physics such as topological matters. In this talk, I will present the state-of-the-part and recent development in orbitronics and outlook and future directions of this new emerging field.