Scanning With a Twist...


How it works: illustration of the quantum twisting microscope in action. Electrons tunnel from the probe (inverted pyramid at the top) to the sample (bottom) in several places at once (green vertical lines) in a quantum-coherent manner. (Courtesy: Weizmann Institute of Science)

Topics: Chemistry, Entanglement, Materials Science, Nanotechnology, Quantum Mechanics

When the scanning tunneling microscope debuted in the 1980s, the result was an explosion in nanotechnology and quantum-device research. Since then, other types of scanning probe microscopes have been developed, and together they have helped researchers flesh out theories of electron transport. But these techniques probe electrons at a single point, thereby observing them as particles and only seeing their wave nature indirectly. Now, researchers at the Weizmann Institute of Science in Israel have built a new scanning probe – the quantum twisting microscope – that detects the quantum wave characteristics of electrons directly.

“It’s effectively a scanning probe tip with an interferometer at its apex,” says Shahal Ilani, the team leader. The researchers overlay a scanning probe tip with ultrathin graphite, hexagonal boron nitride, and a van der Waals crystal such as graphene, which conveniently flopped over the tip like a tent with a flat top about 200 nm across. The flat end is key to the device’s interferometer function.  Instead of an electron tunneling between one point in the sample and the tip, the electron wave function can tunnel across multiple points simultaneously.

“Quite surprisingly, we found that the flat end naturally pivots so that it is always parallel with the sample,” says John Birkbeck, the corresponding author of a paper describing this work. This is fortunate because any tilt would alter the tunneling distance and hence strength from one side of the plateau to the other. “It is the interference of these tunneling paths, as identified in the measured current, that gives the device its unique quantum-wave probing function,” says Birkbeck.

Scanning probe with a twist observes the electron’s wavelike behavior, Anna Demming, Physics World

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