Spintronics without magnetism

Abstract

The spin-orbit effect is at the heart of efforts to merge spintronics-where information is carried and stored by spin, rather than by charge-with semiconductor technology. Subject Areas: SpintronicsThe 2007 Nobel Prize in Physics (awarded to Albert Fert and Peter Grünberg) highlighted the remarkably rapid transition of "spintronics" from fundamental studies of spin-dependent transport in metallic ferromagnetic multilayers [1] to a device technology critical to the magnetic storage industry. While the mainstream of spintronics continues to expand the scientific and technological frontiers of ferromagnetic metal devices [2], a parallel effort in semiconductor spintronics is growing vigorously [3]. This incarnation of spintronics has the same general motivation as metallic spintronics: to understand and control the transport of spin-polarized currents and to eventually apply this knowledge in information technologies. However, semiconductor spintronics also brings with it the promise of integrating the best qualities of two disparate worlds: the unparalleled storage capacity of magnetic memory and the impressive computing power of semiconductor logic. Add to this the possibility of exploiting the relatively long-lived quantum coherence of spin states in semiconductors [4] and one can even imagine unleashing the full power of the quantum world in truly revolutionary devices that exploit both the amplitude and phase of wave functions. Needless to say, the realization of this potential requires concerted efforts aimed at both understanding the mechanisms for spindependent transport in semiconductors as well as critically comparing spin-based device schemes with existing technologies [5].At first glance, it seems almost a given that ferromagnetism would be a necessary and integral component of any scheme for semiconductor spintronic devices. For instance, a semiconductor spintronic device generically requires an imbalance between spin "up" and "down" populations of electrons (or holes). We can imagine this imbalance being created by the injection of spin-polarized charge carriers from a ferromagnet, which acts as a spin polarizer. Alternatively, we could build devices from ferromagnetic semiconductors that have an intrinsic spin imbalance. Indeed, important advances have been made in semiconductor spintronics by using these very notions, with a number of interesting proof-of-concept semiconductor spintronic device demonstrations that incorporate ferromagnetic elements for injecting, detecting, and manipulating spins [6]. But, discoveries in recent years have inspired a completely different avenue to semiconductor spintronics-one that does not involve any ferromagnetism whatsoever [7][8][9].The development of this alternate track-"spintronics without magnetism"-relies on our ability to manipulate carrier spins in semiconductors through the spin-orbit interaction. This is an attractive pathway for designing semiconductor spintronic devices because spin-orbit coupling enables the generation and manipulation of spins solel...

Current-induced spin–orbit torques

“…Together with other forms of spin accumulation and spin currents that can be excited in semiconductors by electrical or optical means, this has generated considerable interest in a 'magnetfree' approach to spintronics [14]. Moreover, several proposals have been made to exploit the intrinsic SO fields in semiconductors to control or modulate spin injection into FM electrodes through a semiconductor channel [62][63][64] or tunnel junction [31,65,66].…”

“…It is only in the last 2 years, however, that current-induced SO-effective magnetic fields have been predicted to occur in ferromagnets [15][16][17] and their existence demonstrated in dilute magnetic semiconductors [18] and ultrathin metal films [19]. Such investigations bridge two of the main research areas in spintronics, the one based on magnetic multi-layer devices [20] and the one 'without magnetism' based on the manipulation of the electron spin in non-magnetic conductors [14]. The observation of strong SO torques at room temperature combined with the simple layer structure and robust FM properties of metal films [19] open a promising new avenue to manipulate the magnetization of spintronic devices by means of electric currents.…”

“…Although it exploits both the flow of a spin-polarized current and static electric fields, such a torque is fundamentally different from the processes described above, relying on the presence of strong SO coupling intrinsic to the nuclear composition and atomic structure of a material. The correlation between charge current and spin polarization arising from the SO interaction has been extensively studied in non-magnetic semiconductors since the 1970s [9][10][11] and recently reviewed by Ganichev & Prettl [12], Silsbee [13] and Awschalom & Samarth [14]. It is only in the last 2 years, however, that current-induced SO-effective magnetic fields have been predicted to occur in ferromagnets [15][16][17] and their existence demonstrated in dilute magnetic semiconductors [18] and ultrathin metal films [19].…”

Intrinsic contribution to spin Hall and spin Nernst effects in a bilayer graphene

“…This effect, known now as the spin Hall effect (SHE) 3 , was studied extensively in the last few years [3][4][5][6][7][8][9] , and is still of current interest -mainly because it offers a new possibility of spin manipulation with electric field only. The possibility of pure electrical manipulation of spin degrees of freedom is interesting not only from fundamental reasons, but also from the point of view of possible applications in future spintronics devices and information processing technologies [10][11][12][13] .…”

Probing the Rashba effect via the induced magnetization around a Kondo impurity

“…1 Interestingly enough, the Rashba spin-orbit (SO) interaction 2 has become one of the intriguing and desired ingredients of modern nanoelectronics and spintronics. 3 Studying the Rashbainduced effects for atoms placed on surfaces is especially interesting, because on one hand, it opens up a way to probe the strength of the SO coupling, and on the other hand, it may allow one to explore the interplay between the Kondo screening and the SO interaction. In this regard, the Au(111) surface is very promising, since it exhibits a measurable energy splitting of surface band states, which was first experimentally observed by LaShell et al [4].…”