Transistor gives nanotech a new spin

TEXAS A&M (US) — Researchers have successfully developed a realistic spin-field-effect transistor that is operable at high temperatures. The design is based on an electron’s spin.

“One of the major stumbling blocks was that to manipulate spin, one may also destroy it,” says Jairo Sinova, professor of physics at Texas A&M University.

“It has only recently been realized that one could manipulate it without destroying it by choosing a particular set-up for the device and manipulating the material.

“One also has to detect it without destroying it, which we were able to do by exploiting our findings from our study of the spin Hall effect six years ago. It is the combination of these basic physics research projects that has given rise to the first spin-FET.”

The research is reported in the journal Science.

Sixty years after the transistor’s discovery, its operation is still based on the physical principles of electrical manipulation and detection of electronic charges in a semiconductor, says Jorg Wunderlich of the Hitachi Cambridge Laboratory.

Subsequent technology has focused on down-scaling the device size, succeeding to the point where scientists are approaching the ultimate limit, shifting the focus to establishing new physical principles of operation to overcome them—specifically, using its elementary magnetic movement, or so-called “spin,” as the logic variable instead of the charge.

The field of “spintronics” promises potential advances in low-power electronics, hybrid electronic-magnetic systems, and completely new functionalities, the researchers say.

The 20-year-old theory of electrical manipulation and detection of electron’s spin in semiconductors has proven to be unexpectedly difficult to experimentally realize.

“We recently discovered quantum-relativistic phenomena for both spin manipulation and detection to realize and confirm all the principal phenomena of the spin transistor concept,” Wunderlich explains.

To observe the electrical manipulation and detection of spins, the team made a specially designed planar photo-diode placed next to the transistor channel.

By shining light on the diode, they injected photo-excited electrons, rather than the customary spin-polarized electrons, into the transistor channel. Voltages were applied to input-gate electrodes to control the procession of spins via quantum-relativistic effects.

These effects—attributable to quantum relativity—are also responsible for the onset of transverse electrical voltages in the device, which represent the output signal, dependent on the local orientation of processing electron spins in the transistor channel.

The new device can have a broad range of applications in spintronics research as an efficient tool for manipulating and detecting spins in semiconductors without disturbing the spin-polarized current or using magnetic elements.

The observed output electrical signals remain large at high temperatures and are linearly dependent on the degree of circular polarization of the incident light, Wunderlich says.

The device therefore represents a realization of an electrically controllable solid-state polarimeter which directly converts polarization of light into electric voltage signals. He says future applications may exploit the device to detect the content of chiral molecules in solutions, for example, to measure the blood-sugar levels of patients or the sugar content of wine.

The new research is expected to shift the focus from the theoretical academic speculation to prototype microelectronic device development.

Scientists from the University of Nottingham, the University of Cambridge, the Academy of Sciences, and Charles University in the Czech Republic contributed to the research.

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