Jairo Sinova

Anomalous Hall effect

We present a review of experimental and theoretical studies of the anomalous Hall effect (AHE), focusing on recent developments that have provided a more complete framework for understanding this subtle phenomenon and have, in many instances, replaced controversy by clarity. Synergy between experimental and theoretical work, both playing a crucial role, has been at the heart of these advances. On the theoretical front, the adoption of Berry-phase concepts has established a link between the AHE and the topological nature of the Hall currents which originate from spin-orbit coupling. On the experimental front, new experimental studies of the AHE in transition metals, transition-metal oxides, spinels, pyrochlores, and metallic dilute magnetic semiconductors, have more clearly established systematic trends. These two developments in concert with first-principles electronic structure calculations, strongly favor the dominance of an intrinsic Berry-phase-related AHE mechanism in metallic ferromagnets with moderate conductivity. The intrinsic AHE can be expressed in terms of Berry-phase curvatures and it is therefore an intrinsic quantum mechanical property of a perfect cyrstal. An extrinsic mechanism, skew scattering from disorder, tends to dominate the AHE in highly conductive ferromagnets. We review the full modern semiclassical treatment of the AHE together with the more rigorous quantum-mechanical treatments based on the Kubo and Keldysh formalisms, taking into account multiband effects, and demonstrate the equivalence of all three linear response theories in the metallic regime. Finally we discuss outstanding issues and avenues for future investigation.

Universal Intrinsic Spin Hall Effect

We describe a new effect in semiconductor spintronics that leads to dissipationless spin currents in paramagnetic spin-orbit coupled systems. We argue that in a high-mobility two-dimensional electron system with substantial Rashba spin-orbit coupling, a spin current that flows perpendicular to the charge current is intrinsic. In the usual case where both spin-orbit split bands are occupied, the intrinsic spin-Hall conductivity has a universal value for zero quasiparticle spectral broadening.

Theory of ferromagnetic (III,Mn)V semiconductors

The body of research on (III,Mn)V diluted magnetic semiconductors initiated during the 1990s has concentrated on three major fronts: i) the microscopic origins and fundamental physics of the ferromagnetism that occurs in these systems, ii) the materials science of growth and defects and iii) the development of spintronic devices with new functionalities. This article reviews the current status of the field, concentrating on the first two, more mature research directions. From the fundamental point of view, (Ga,Mn)As and several other (III,Mn)V DMSs are now regarded as textbook examples of a rare class of robust ferromagnets with dilute magnetic moments coupled by delocalized charge carriers. Both local moments and itinerant holes are provided by Mn, which makes the systems particularly favorable for realizing this unusual ordered state. Advances in growth and post-growth treatment techniques have played a central role in the field, often pushing the limits of dilute Mn moment densities and the uniformity and purity of materials far beyond those allowed by equilibrium thermodynamics. In (III,Mn)V compounds, material quality and magnetic properties are intimately connected. In the review we focus on the theoretical understanding of the origins of ferromagnetism and basic structural, magnetic, magneto-transport, and magneto-optical characteristics of simple (III,Mn)V epilayers, with the main emphasis on (Ga,Mn)As. The conclusions we arrive at are based on an extensive literature covering results of complementary ab initio and effective Hamiltonian computational techniques, and on comparisons between theory and experiment.

Experimental observation of the spin-hall effect in a two-dimensional spin-orbit coupled semiconductor system

We report the experimental observation of the spin-Hall effect in a 2D hole system with spin-orbit coupling. The 2D hole layer is a part of a p-n junction light-emitting diode with a specially designed coplanar geometry which allows an angle-resolved polarization detection at opposite edges of the 2D hole system. In equilibrium the angular momenta of the spin-orbit split heavy-hole states lie in the plane of the 2D layer. When an electric field is applied across the hole channel, a nonzero out-of-plane component of the angular momentum is detected whose sign depends on the sign of the electric field and is opposite for the two edges. Microscopic quantum transport calculations show only a weak effect of disorder, suggesting that the clean limit spin-Hall conductance description (intrinsic spin-Hall effect) might apply to our system. The Hall effects are among the most recognized families of phenomena in basic physics and applied microelectronics. The ordinary and quantum Hall effects, which, e.g., proved the existence of positively charged carriers (holes) in semiconductors and led to the discovery of fractionally charged quasiparticles [1], occur due to the Lorentz force that deflects like-charge carriers towards one edge of the sample creating a voltage transverse to the current. In the anomalous Hall effect [2], the spin-orbit interaction plays the role of the force that deflects like-spin carriers to one edge and opposite spins to the other edge of the sample. In a ferromagnetic material this leads to a net charge imbalance between the two sides which allows one to detect magnetization in the conductor by simple electrical means. Here we report the experimental observation of a new member of the Hall family —the spin-Hall effect (SHE). As an analogue of the anomalous Hall effect but realized in nonmagnetic systems, the SHE opens new avenues for inducing and controlling spin currents in semiconductors without applying magnetic fields or introducing ferromagnetic elements. Predictions of the SHE were reported, within different physical contexts, in several seminal studies [3‐6], and currently its microscopic origins are the subject of an intense theoretical debate [7‐18]. Experimentally, the SHE has been elusive because in nonmagnetic systems the transverse spin currents do not lead to net charge imbalance across the sample, precluding the simple electrical measurement. To demonstrate the SHE, we have developed a novel p-n junction light-emitting diode (LED) microdevice, in a similar spirit to the one proposed in Ref. [5] but distinct in that it couples two-dimensional hole and electron doped systems. Its coplanar geometry and the strong spin-orbit (SO) coupling in the embedded two-dimensional hole gas (2DHG), whose ultrasmall thickness diminishes current induced self-field effects, are well suited for inducing and detecting the SHE. When an electric field is applied across the hole layer, a nonzero out-of-plane component of the spin is optically detected whose sign depends on the sign of the field and is opposite for the two edges, consistent with theory

Prospects for high temperature ferromagnetism in (Ga,Mn)As semiconductors

We report on a comprehensive combined experimental and theoretical study of Curie temperature trends in (Ga,Mn)As ferromagnetic semiconductors. Broad agreement between theoretical expectations and measured data allows us to conclude that

First Principles Calculation of Anomalous Hall Conductivity in Ferromagnetic bcc Fe

{T}_{c}

New moves of the spintronics tango

in high-quality metallic samples increases linearly with the number of uncompensated local moments on

Spin Hall effect transistor.

{\mathrm{Mn}}_{\mathrm{Ga}}

Curie Temperature Trends in (III,Mn)V Ferromagnetic Semiconductors

acceptors, with no sign of saturation. Room temperature ferromagnetism is expected for a 10% concentration of these local moments. Our magnetotransport and magnetization data are consistent with the picture in which Mn impurities incorporated during growth at interstitial

Relativistic Néel-order fields induced by electrical current in antiferromagnets.

{\mathrm{Mn}}_{\mathrm{I}}