Hydrodynamic electron flow relies on strong interactions between electrons, just as water and other fluids rely on strong interactions between their particles. In order to flow efficiently, electrons in high density materials arrange themselves in such a way that limits interactions. It’s the same reason that group dances like the electric slide don’t involve a lot of interaction between dancers — with that many people, it's easier for everyone to do their own moves.
“To date, hydrodynamic effects have mostly been deduced from transport measurements, which effectively jumbles up the spatial signatures,” said Yacoby. “Our work has charted a different path in observing this dance and understanding hydrodynamics in systems beyond graphene with new quantum probes of electron correlations.”
The researchers proposed that rather than direct interactions, electrons in high density materials could interact with one another through the quantum vibrations of the atomic lattice, known as phonons.
“We can think of the phonon-mediated interactions between electrons by imagining two people jumping on a trampoline, who don’t propel each other directly but rather via the elastic force of the springs,” said Yaxian Wang, a postdoctoral scholar in the NarangLab at SEAS and co-author of the study.
In order to observe this mechanism, the researchers developed a new cryogenic scanning probe based on the nitrogen-vacancy defect in diamond, which imaged the local magnetic field of a current flow in a material called layered semimetal tungsten ditelluride.
“Our tiny quantum sensor is sensitive to small changes in the local magnetic field, allowing us to explore the magnetic structure in a material directly,” said Uri Vool, John Harvard distinguished science fellow and co-lead author of the study.
Not only did the researchers find evidence of hydrodynamic flow within three-dimensional tungsten ditelluride but they also found that the hydrodynamic character of the current strongly depends on the temperature.
“Hydrodynamic flow occurs in a narrow regime where temperature is not too high and not too low, and so the unique ability to scan across a wide temperature range was crucial to see the effect,” said Assaf Hamo, a postdoctoral scholar at the Yacoby lab and co-lead author of the study.
“The ability to image and engineer these hydrodynamic flows in three-dimensional conductors as a function of temperature, opens up the possibility to achieve near dissipation-less electronics in nanoscale devices, as well as provides new insights into understanding electron-electron interactions,” said Georgios Varnavides, a Ph.D student in the NarangLab at SEAS and one of the lead authors of the study. ”The research also paves the way for exploring non-classical fluid behavior in hydrodynamic electron flow, such as steady-state vortices.”
“This is an exciting and interdisciplinary field synthesizing concepts from condensed matter and materials science to computational hydrodynamics and statistical physics,” said Narang. In previous research, Varnavides and Narang classified different types of hydrodynamic behaviors which could arise in quantum materials where electrons flow collectively.
This research was co-authored by Tony X. Zhou, Nitesh Kumar, Yuliya Dovzhenko, Ziwei Qiu, Christina A. C. Garcia, Andrew T. Pierce, Johannes Gooth, Polina Anikeeva, and Claudia Felser. It was supported in part by the US Department of Energy (DOE), Basic Energy Sciences Office, Division of Materials Sciences and Engineering, under award DE-SC0019300, Army Research Office grant no. W911NF-17-1-0023 and Army Research Office MURI (Ab-Initio Solid-State Quantum Materials) grant no. W911NF-18-1-0431 as well as the Gordon and Betty Moore Foundation through an EPiQS Initiative grant no. GBMF4531 and Moore Inventor Fellowship grant no.GBMF8048.
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September 14, 2021 at 07:00PM
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First glimpse of hydrodynamic electron flow in 3D materials - Harvard School of Engineering and Applied Sciences
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