The Science of the Speedy Switch

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The magnetite experiment was conducted at the Soft X-ray Materials Science (SXR) experimental station at SLAC National Accelerator Laboratory's Linac Coherent Light Source X-ray laser.Photo courtesy of Brad Plummer/SLAC

The magnetite experiment was conducted at the Soft X-ray Materials Science (SXR) experimental station at SLAC National Accelerator Laboratory's Linac Coherent Light Source X-ray laser.

Switches are rarely simple, or speedy. Ask anyone who has switched a major … or a school … or even a career. Yet they're often essential too. Ask anyone who has switched a major … or a school … or a career.

In a real sense, a switch serves as the foundation for the entire electronic world. Not "On" and "Off" buttons (though the latter can be pretty important too), but rather the transistor, the tiny but mighty on/off switch that makes up the core of everything from massive exascale computers to mobile electronic devices.

Since silicon transistors are approaching basic limits of size and speed, researchers have begun to look at other materials that might serve in their stead. Recently, a group of researchers at the Office of Science's SLAC National Accelerator Laboratory discovered an ultrafast electrical switch, which might eventually lead to a switch to faster and even more powerful computers.

The ultrafast switch came from one of the oldest-known magnetic materials, magnetite. (Magnetite was also the material used in the first compass.) Researchers found that they could make magnetite flip from "on" to "off" in 1 trillionth of a second. That's 0.000000000001 of a second, or about 3-4 million eye-blinks (assuming eye-blinks of about 300-400 milliseconds); and thousands of times faster than the transistors we encounter every day.

Measuring such a swift switch took serious doing, and so SLAC scientists turned to a high-tech tool, the Linac Coherent Light Source (LCLS) X-ray laser. They first blasted the magnetite with a visible-light laser, and then followed the strike with an X-ray pulse of great precision and power. Doing so allowed researchers to not only measure the speed of the switch, but also to image what actually caused it.

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In its insulating state, the magnetite sample has electrical charges locked into structures known as Photo courtesy of S. de Jon et al./Nature Materials

In its insulating state, the magnetite sample has electrical charges locked into structures known as "trimerons" that are composed of three iron atoms (a). An optical laser pulse was used to fracture trimerons (b), creating strands of electrical conductivity (red) surrounding islands of non-conducting trimeron structures (c).

Previous research had shown that magnetite acquires its electronic properties from an arrangement of three iron atoms known as a trimeron. SLAC researchers showed that trimerons can be switched from "on" to "off" in less than a flash (hundredths of quadrillionths of a second – don't even try to write out all the zeros). This turns the material from an insulator to a conductor since the remaining trimerons then rearrange from a fence-like structure through which few electrons can wander into a relatively open field though which electrons can run freely, thus carrying charges (even as other portions of the material remain as non-conducting "islands").

Admittedly, Silicon Valley won't become Magnetite Meadow anytime soon. That's because the samples had to be cooled to -190 Celsius (-310 Fahrenheit) to lock in the charges. But the experiment opens new possibilities in materials that might eventually lead to a switch from silicon. For instance, SLAC researchers are exploring if vanadium dioxide can be coaxed to make the same trillionth-of-a-second switch, but at something closer to room temperature. Other materials may also be found.

The post-silicon possibilities are starting to open. That's thanks to dedicated researchers at SLAC, and their science of the speedy switch.

The Department's Office of Science is the single largest supporter of basic research in the physical sciences in the United States and is working to address some of the most pressing challenges of our time. For more information please visit http://science.energy.gov/about. For more information about SLAC National Accelerator Laboratory, please go to: http://www6.slac.stanford.edu/.

Charles Rousseaux is a Senior Writer in the Office of Science, [email protected].