Transport at Nanoscale Interfaces

Education

Electron hydrodynamics in graphene heterostructures

Hydrodynamics is the branch of physics dealing with the motion of fluids and the forces of interaction therein. In low-dimensional systems and at reduced temperatures, a hydrodynamic regime of transport, with heat and charge flow replicating the behavior of fluids, has been predicted and experimentally observed1-3. However, observing the hydrodynamic regime is not simple as it requires extremely clean, disorder-free channels. This condition eliminates most materials with large inherent scattering, which demonstrate diffusive transport. Graphene, on the other hand, with its two-dimensional nature and high mobility (indicative of a low-disorder), is an ideal candidate for hydrodynamic transport, making it the material of choice for the project2.


The aim of this project is the experimental verification of hydrodynamic signatures in graphene devices. We will be working with graphene and/or twisted bilayer graphene channels encapsulated in hexagonal boron nitride (h-BN). h-BN is a two-dimensional insulator with a lattice structure similar to graphene and acts both as a defect-free sub- strate and protective layer for the graphene channel. This prevents contamination of the graphene channel during fabrication and enhances the chances of observing hydrodynamic behavior. We will be performing electrical (in a non-local geometry) and magnetic field (magnetoresistance and Hall) characterization of the devices at low tem- peratures (< 70 K) aimed at verifying the presence of a hydrodynamic regime.


The student will fabricate the samples and perform the transport measurements. It will be an opportunity to gain experience in the innovative techniques of modern nanofabrication and measurement practices at cryogenic tem- peratures, along with the chance to work in an emerging field of physics, which is both theoretically intriguing and promises to grow in importance as devices scale down in size.


We invite applications from highly motivated students with a strong background in physics, nanoscience, electrical engineering or related fields. We provide state-of-the-art facilities and an ideal environment for conducting your research.


For more information, please contact Tathagata Paul (tathagata.paul@empa.ch). For applications, please send a short motivation (including educational background and exam grades).

References

1De Jong, M. J. M., and L. W. Molenkamp. "Hydrodynamic electron flow in high-mobility wires." Physical Review B 51.19 (1995): 13389.
2 Bandurin, D. A., et al. "Negative local resistance caused by viscous electron backflow in graphene." Science 351.6277 (2016): 1055-1058.
3 Gooth, J., et al. "Thermal and electrical signatures of a hydrodynamic electron fluid in tungsten diphosphide." Nature communi- cations 9.1 (2018): 1-8.
a Image clicked by Oliver Braun, Empa.