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Researchers use electron spin to measure time without a clock

Electron spin measures time. When light strikes an object, the object emits electrons. Cool, huh? This phenomenon, known as photoemission, occurs with solids, gases, and liquids. When Albert Einstein discovered it back in 1905, it won him the Nobel Prize.

Photoemission isn’t the end of the story, though. Scientists have been working to study the timescales of photoemission. Do electrons become excited at the exact moment – and we’re talking moments in terms of attoseconds, here – that the light hits the surface of the material, or is there a time delay?

To find out, scientists didn’t use a clock. Instead, they studied the spin polarization of emitted electrons. The spin of an electron is what makes a particle seems as though it’s rotating around its axis. Meanwhile, spin polarization refers to the degree to which this acid is aligned towards a given direction.

In a new study, Mauro Fanciulli and a team at EPFL showed a connection between spin polarization of emitted electrons and attosecond time delays during photoemission. The researchers used photoemission spectroscopy (SARPES) to get spin measurements on electrons emitted from a crystal of copper.

Fanciulli, first author of the study, explains why the findings are so significant.

“With lasers you can directly measure the time delay between different processes, but it is difficult to determine when a process starts – time zero,” he said. ”But in our experiment we measure time indirectly, so we don’t have that problem – we could access one of the shortest timescales ever measured. The two techniques [spin and lasers], are complementary, and together they can yield a whole new realm of information.”

Another member of the team, Hugo Dil, elaborates: ”It deals with the fundamental nature of time itself and will help understand the details of the photoemission process, but it can also be used in photoemission spectroscopy on materials of interest.”

What materials does he have in mind? His team plans to study grapheme – an atom-thin layer of pure carbon – as well as high-temperature superconductors.

The current study was published in the journal Physical Review.

By Dawn Henderson, Staff Writer

Source: Mauro Fanciulli and Hugo Dil, EPFL

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