October 20, 2009

Electron Spin Controlled with Electric Fields

The holy grail in spintronics is to address spin with something other than magnets and now University of Ohio researchers provided a theoretical modeling for a recent experiment that was the first to successfully control an electron’s spin using purely electrical fields.

The team collaborated with a research group at the University of Cincinnati, led by Philippe Debray and Marc Cahay. Debray conceived and designed the experiments. The Ohio University researchers’ calculations explained the behavior of the electrons in Debray’s experimental conditions and predicted how strong the electric field’s control over the spin would be.

Their research also revealed one of the key conditions of the experiment—that the tiny connection along which the electrons travel in the device must be asymmetrical.

Controlling spin electronically has major implications for the future of novel devices such as transistors, but this experiment is only the first step of many, Ulloa said. The next step would be to rework the experiment so that it could be performed at a higher, more practical temperature not requiring the use of liquid helium.

All-electric quantum point contact spin-polarizer

The controlled creation, manipulation and detection of spin-polarized currents by purely electrical means remains a central challenge of spintronics. Efforts to meet this challenge by exploiting the coupling of the electron orbital motion to its spin, in particular Rashba spin–orbit coupling, have so far been unsuccessful. Recently, it has been shown theoretically that the confining potential of a small current-carrying wire with high intrinsic spin–orbit coupling leads to the accumulation of opposite spins at opposite edges of the wire, though not to a spin-polarized current. Here, we present experimental evidence that a quantum point contact—a short wire—made from a semiconductor with high intrinsic spin–orbit coupling can generate a completely spin-polarized current when its lateral confinement is made highly asymmetric. By avoiding the use of ferromagnetic contacts or external magnetic fields, such quantum point contacts may make feasible the development of a variety of semiconductor spintronic devices.

17 pages of supplemental information

Nanoscale and Quantum Phenomena Institute (NQPI) Web site of Ohio University

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