Jörg Wunderlich

Spin Hall effect devices

The spin Hall effect is a relativistic spin-orbit coupling phenomenon that can be used to electrically generate or detect spin currents in non-magnetic systems. Here we review the experimental results that, since the first experimental observation of the spin Hall effect less than 10 years ago, have established the basic physical understanding of the phenomenon, and the role that several of the spin Hall devices have had in the demonstration of spintronic functionalities and physical phenomena. We have attempted to organize the experiments in a chronological order, while simultaneously dividing the Review into sections on semiconductor or metal spin Hall devices, and on optical or electrical spin Hall experiments. The spin Hall device studies are placed in a broader context of the field of spin injection, manipulation, and detection in non-magnetic conductors.

Spin Hall effect transistor.

In a Spin Hall The spin Hall effect, in which an electrical current causes accumulation of electron spins of opposite signs in the direction transverse to the current flow, provides a promising avenue of research in exploiting the spin degree of freedom in electronic devices. However, implementing the effect in a device is challenging. Wunderlich et al. (p. 1801) combine the concept of the spin Hall effect with that of a spin transistor, and build a nonmagnetic device in a which a spin current, injected by optical means, is “stripped” of its charge component, goes through a spin-modulation layer, and is detected using the inverse spin Hall effect. Such manipulation of the spin current may help in future spintronic applications. Manipulation of the spin degree of freedom of electrons is used to build a spin transistor without magnetic materials. The field of semiconductor spintronics explores spin-related quantum relativistic phenomena in solid-state systems. Spin transistors and spin Hall effects have been two separate leading directions of research in this field. We have combined the two directions by realizing an all-semiconductor spin Hall effect transistor. The device uses diffusive transport and operates without electrical current in the active part of the transistor. We demonstrate a spin AND logic function in a semiconductor channel with two gates. Our study shows the utility of the spin Hall effect in a microelectronic device geometry, realizes the spin transistor with electrical detection directly along the gated semiconductor channel, and provides an experimental tool for exploring spin Hall and spin precession phenomena in an electrically tunable semiconductor layer.

Anisotropic Magnetoresistance Components in (Ga,Mn)As

We explore the basic physical origins of the noncrystalline and crystalline components of the anisotropic magnetoresistance (AMR) in (Ga,Mn)As. The sign of the noncrystalline AMR is found to be determined by the form of spin-orbit coupling in the host band and by the relative strengths of the nonmagnetic and magnetic contributions to the Mn impurity potential. We develop experimental methods yielding directly the noncrystalline and crystalline AMR components which are then analyzed independently. We report the observation of an AMR dominated by a large uniaxial crystalline component and show that AMR can be modified by local strain relaxation. Generic implications of our findings for other dilute moment systems are discussed.

Spin-injection Hall effect in a planar photovoltaic cell

A technique that allows the electrical detection of spin-polarized transport in semiconductors without disturbing the spin-polarized current or using magnetic elements has now been demonstrated. The approach could lead to the integration of spintronics elements into semiconductor microelectronic circuits.

Spintronics: Current-switched magnetic insulator

Exploiting the spin Hall effect acting on magnetic oxides outlines an unprecedented path towards low-power, non-volatile spintronics devices.

Spintronics: Electrons act constructively

Interference effects in semiconductor quantum structures provide an elegant way to electrically map the strength and direction of spin–orbit fields.