Physicists at MIT and the Weizmann Institute of Science have visualized eddies in an electron fluid. This is the first time they have observed electrons flowing in vortices, or eddies, the hallmarks of hydrodynamic flow.
Theorists have long predicted electron eddies or vortices, but they had never been seen before. Now, physicists have seen it, and it is a clear sign of being in this new regime, where electrons behave like a fluid, not like individual particles.
Leonid Levitov, a physics professor at MIT, said: “We know when electrons pass in a fluid state, [energy] dissipation falls, and this interests designing low-power electronics. This new observation is a further step in this direction. “
In 2017, Levitov and colleagues at the University of Manchester detected signs of fluid-like electron behavior in graphene. They engraved a thin channel on a sheet of graphene with several pinch points. Sending current through the channel could also flow through low-strength constrictions.
This suggested that current electrons could pass through pinch points collectively, like a fluid, rather than clogging like individual grains of sand.
This discovery inspired Levitov to find other phenomena of electronic fluids. In this new study, physicists tried to visualize electron vortices.
The authors noted that “the most striking and ubiquitous feature of regular fluid flow, the formation of vortices and turbulence, has not yet been observed in electronic fluids despite numerous theoretical predictions.”
Subtitle: In most materials such as gold (left), electrons flow with the electric field. But MIT physicists have discovered that in exotic (right) tungsten ditelluride, particles can reverse direction and spin like a liquid. Credits: courtesy of the researchers
For visualization, the team used tungsten dithelide (WTe2), one of the new quantum materials where electrons interact strongly and behave like quantum waves instead of particles. They began by synthesizing pure simple crystals of tungsten ditelide and exfoliating thin flakes of the material.
Later, using electron beam lithography and plasma etching techniques, they modeled each scale on a central channel connected to a circular chamber on either side. The same pattern was engraved on fine gold flakes.
They then ran through the modeled sample at very low temperatures of 4.5 kelvins (about -450 degrees Fahrenheit). Using a nanoscale superconducting quantum interference (SQUID) interference device at one end, they could measure current flow at specific points in each sample. SQUID allows the equipment to see the flow of electrons through the modeled channels.
They found that electrons flowing through channels stamped in gold flakes did so without reversing direction, even when some currents passed through each side chamber before reuniting with the main current. Instead, electrons flowing through the tungsten ditelluride flowed through the channel and rotated in each side chamber, just as water would when emptied into a bowl. Electrons created small eddies in each chamber before returning to the main channel.
Levitov said: “We noticed a change in the direction of the flow in the chambers, where the direction of the flow reversed the direction compared to that of the central strip. This is a very surprising thing, and it is the same physics as the of ordinary fluids, but that happens with electrons at the nanoscale. This is a clear sign that electrons are in a fluid – like regime. “
“The findings represent experimental confirmation of a fundamental property in the behavior of electrons. They may also explain how engineers could design low-power devices that conduct more fluid, less resistive electricity.”
Klaus Ensslin, a physics professor at ETH Zurich in Switzerland who did not participate in the study, said: “Signatures of viscous electron flux have been reported in several experiments with different materials. It has now been confirmed. experimentally the theoretical expectation of vortex-like current flow, which adds an important milestone in the investigation of this new transport regime. “
Magazine reference:
- Aharon-Steinberg, A., Völkl, T., Kaplan, A. et al. Direct observation of vortex in an electronic fluid. Nature 607, 74–80 (2022). DOI: 10.1038 / s41586-022-04794-y