Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.

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Spintronics: Fundamentals and applications

We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

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Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

The 1937 theoretical discovery of Majorana fermions-whose defining property is that they are their own anti-particles-has since impacted diverse problems ranging from neutrino physics and dark matter searches to the fractional quantum Hall effect and superconductivity. Despite this long history the unambiguous observation of Majorana fermions nevertheless remains an outstanding goal. This review paper highlights recent advances in the condensed matter search for Majorana that have led many in the field to believe that this quest may soon bear fruit. We begin by introducing in some detail exotic 'topological' one- and two-dimensional superconductors that support Majorana fermions at their boundaries and at vortices. We then turn to one of the key insights that arose during the past few years; namely, that it is possible to 'engineer' such exotic superconductors in the laboratory by forming appropriate heterostructures with ordinary s-wave superconductors. Numerous proposals of this type are discussed, based on diverse materials such as topological insulators, conventional semiconductors, ferromagnetic metals and many others. The all-important question of how one experimentally detects Majorana fermions in these setups is then addressed. We focus on three classes of measurements that provide smoking-gun Majorana signatures: tunneling, Josephson effects and interferometry. Finally, we discuss the most remarkable properties of condensed matter Majorana fermions-the non-Abelian exchange statistics that they generate and their associated potential for quantum computation.

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New directions in the pursuit of Majorana fermions in solid state systems.

Electrically induced electron-spin polarization near the edges of a semiconductor channel was detected and imaged with the use of Kerr rotation microscopy The polarization is out-of-plane and has opposite sign for the two edges, consistent with the predictions of the spin Hall effect Measurements of unstrained gallium arsenide and strained indium gallium arsenide samples reveal that strain modifies spin accumulation at zero magnetic field A weak dependence on crystal orientation for the strained samples suggests that the mechanism is the extrinsic spin Hall effect

https://science.sciencemag.org/content/sci/306/5703/1910.full.pdf

Observation of the spin Hall effect in semiconductors.

Superconducting circuits are macroscopic in size but have generic quantum properties such as quantized energy levels, superposition of states, and entanglement, all of which are more commonly associated with atoms. Superconducting quantum bits (qubits) form the key component of these circuits. Their quantum state is manipulated by using electromagnetic pulses to control the magnetic flux, the electric charge or the phase difference across a Josephson junction (a device with nonlinear inductance and no energy dissipation). As such, superconducting qubits are not only of considerable fundamental interest but also might ultimately form the primitive building blocks of quantum computers.

Superconducting quantum bits

PROBLEM TO BE SOLVED: To make it possible to control an electromagnetic field environment which influences the characteristic of a minute tunnel junction greatly, by uniting the minute tunnel junction with a two-dimensional electron gas in first and second heteroconstruction semiconductors. SOLUTION: A semiconductor heterojunction 51 containing an indium arsenic layer for forming a two-dimensional electron gas is grown by a molecular beam epitaxy method on an insulating substrate 55 made out of indium phosphorus, and layers being more above than an InAs layer are removed by etching, and a metal-two-dimensional electron gas contact part 56 is formed. A minute tunnel junction-two-dimensional electron gas (2DEG) contact part is for bringing a minute tunnel junction into contact with a 2DEG. It becomes possible to remove excessive quasiparticles from a junction electrode, by putting a normal metal region made out of 2DEG in the vicinity of the minute tunnel junction. As a result of this, it becomes possible to realize a thermally balanced state where the behavior of pairs of coopers in a superconducting state is determined by the band of a base condition.

Semiconductor united single electron tunneling element and its manufacture

We have investigated the values of the Rashba spin-orbit coupling constant a in In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As quantum wells using an anti-weak-localization (AWL) analysis as a function of quantum well asymmetry. We have found that the deduced a values have strong correlations with the structural inversion asymmetry of the pertinent quantum wells as predicted theoretically. This fact suggests that the AWL analysis provides a reliable way to deduce a values experimentally for designing future spintronics devices.

Anti-weak-localization study of Rashba spin-splitting energy as a function of well asymmetry in InAlAs/InGaAs/InAlAs quantum wells

Competition between Two Kinds of Dissipation in a dc-SQUID

Conditions for the Spin Rectification Phenomena Predicted for Semiconducting Triple Barrier Structures in the Presence of Rashba Spin-Orbit Coupling

We successfully distinguished flux qubit states by means of single-shot measurement with a high-resolution dc-SQUID. We studied the readout results of the qubit states for two types of sample (classical and quantum) and found that the classical sample exhibited incoherent macroscopic tunneling between two flux states. With the quantum sample, we directly observed the superposition states of the qubit without microwave-spectroscopy experiments.

Hideaki Takayanagi

Papers

Semiconductor united single electron tunneling element and its manufacture

Anti-weak-localization study of Rashba spin-splitting energy as a function of well asymmetry in InAlAs/InGaAs/InAlAs quantum wells

Competition between Two Kinds of Dissipation in a dc-SQUID

Conditions for the Spin Rectification Phenomena Predicted for Semiconducting Triple Barrier Structures in the Presence of Rashba Spin-Orbit Coupling

Incoherent and Coherent Tunneling of Macroscopic Phase in Flux Qubits