Events at Physics |
Events on Monday, May 19th, 2025
- Academic Calendar
- 4-week summer session begins
- Abstract: *Note: actual end time may vary.*
- Thesis Defense
- Nanoscale imaging of viscous and nonlocal transport of electrons in graphene
- Time: 11:00 am - 1:00 pm
- Place: Chamberlin Hall Room 5310
- Speaker: Zachary Krebs, Physics PhD Graduate Student
- Abstract: Ballistic and hydrodynamic electron flow can develop in materials when carrier momentum is conserved over long distance and time scales. These non-Ohmic transport regimes are characterized by distinctive spatial distributions of the current density and electrochemical potential. I will show scanning tunneling potentiometry (STP) measurements of the electrochemical potential induced by DC transport in graphene as a function of carrier density, temperature, and magnetic field. First, STP images are recorded as current flows through electrostatic constrictions with gate-tunable width that are "drawn" with the STM tip. The electrochemical potential drop through these constrictions determines the wavevector-dependent conductivity σ(k) of the electron fluid. Upon heating the system from 4.5 K to 77 K, enhanced electron-electron scattering leads to a crossover from ballistic to hydrodynamic flow, identified by super-ballistic conductance through the constrictions and a suppression of Landauer residual resistivity dipoles. When increasing the magnetic field from 0 to 1.4 T at 4.5 K, the STP data reveals a diffusive-to-ballistic crossover in the flow of current resulting from Landau level quantization. In the ballistic regime of magnetotransport, the local Hall field is enhanced one cyclotron diameter away from scattering surfaces.
- Host: Victor Brar