Energy-efficient computing and communication devices:
Information encoded in magnets is non-volatile. Namely, once information is written in magnetic bits, external power is not needed to keep it intact. This offers a major advantage in terms of solving the problem of minimizing energy wasted in preserving information in the present-day electronic devices. In this context, discovery of phenomena allowing for manipulating magnetic order via electrical fields and current provides alternative route to constructing magnet-based computing devices. However, large power consumption demanded by this electric control is one major challenge faced by spintronics. One direction we explore to solve this challenge is to engineer high spin-orbit interaction at magnetic interfaces, which provide an energy efficient way to apply spin-orbit torques on magnets via electric currents and electric fields. Towards this goal, we have developed unified models to predict, and observe in close collaboration with experimentalists, electrical field and current induced energy-efficient manipulation of a wide class of magnets for memory and logic functionality.
The major advantage provided by these spin-orbit torques is that the charge current need not pass through the magnetic materials. Consequently, a broad class of even insulating and antiferromagnetic (AFM) materials can be driven out-of-equilibrium. AFM materials are particularly interesting, as they host excitation in THz, thus providing opportunities to build communication devices in the coveted 'THz gap'. We are interested in exploiting spin-orbit control to build such devices. The same spin-orbit interactions allow for coupling thermal fluctuations, which could also be utilized for harvesting thermal energy in creating such devices.
Quantum materials and devices:
Strong spin-orbit interactions also give rise to a new state of matter called topological insulator. Such topological insulators have conducting spin-polarized conduction at their surfaces, while being insulating in the bulk. By marrying such topological insulators to magnets we have observed, in collaboration of experimentalists, record high values of spin-orbit torques. Moreover, such hybrid magnetic and topological insulator systems exhibit a novel quantum phase: quantum anomalous Hall phase (a zero field quantum Hall phase). Such a phase hosts dissipationless unidirectional conduction channels, which can be controlled by controlling magnetic domains. In our group we are interested in utilizing these "quantum materials" to come up with novel schemes for constructing and entangling quantum bits for quantum information processing applications.
Another system of interest, which marrys quantum phenomena to spintronics, is that of single spin qubits (such as NV centers) coupled to magnetic films. Directions of interest in this system are possibilities of creating reconfigurable quantum circuits, where quasi-particles (such as magnons) or spin superfluids in magnetic insulators act as a channel for communicating between single spin qubits.
Biomedical and Bio-inspired devices:
Emergence of Big Data applications, requiring non-Boolean computing in noisy environments with minimal energy dissipation, has led to the development of brain-inspired schemes of computation. The rationale behind this approach being that human brains are ideally suited for such tasks. It is widely believed that present-day electronic devices provide an inefficient (in terms of energy, area and speed) hardware platform for carrying out brain-inspired computing. The challenge here is to find alternate phenomena and material systems for mapping the underlying physics onto non-Boolean tasks. Reciprocally, there is an increasing demand of devices which could "interact" with human body for building brain-machine interfaces and implantable devices, as a means to alter electrical impulses in the body for "electroceutical" applications (as opposed to pharmaceuticals, which bank on altering the state of body chemically) . We believe that the wide class of available magnetic materials exhibiting an impressive set of magneto-electric phenomena discovered in the last decade, in conjunction with the fact that magnetic fields can penetrate most efficiently through human body, make magnets ideal material system suited to meet the demand of this application space. We are interested in exploring application of spintronics for constructing such biomedical and bio-inspired devices within this theme.
Spin-orbit torque-induced creation and motion of skyrmions for skyrmion-based memory and logic Science 349, 6245 (2015) LINK
(Left panel) Single spins, by interacting with magnetic films, act as nano-sized quantum sensors of magnetic fluctuations Science 357, 6347 (2017) LINK (Right panel) Uni-directional modes in a quantum anomalous Hall phase provide dissipationless quantum channels for building quantum information processing devices. Phys. Rev. B, Rapid Comm. 94, 020411 (2016) LINK
Magnetic fields, by penetrating the deepest, interact most efficiently with the human body [figure taken from Nature Rev. Mat. 2, 16093 (2017)]