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VERSION:2.0
CALSCALE:GREGORIAN
PRODID:UW-Madison-Physics-Events
BEGIN:VEVENT
SEQUENCE:2
UID:UW-Physics-Event-9206
DTSTART:20250519T160000Z
DTEND:20250519T180000Z
DTSTAMP:20260413T135817Z
LAST-MODIFIED:20250515T194130Z
LOCATION:5310 CH or https://uwmadison.zoom.us/j/95605476727
SUMMARY:Nanoscale imaging of viscous and nonlocal transport of electro
 ns in graphene\, Thesis Defense\, Zachary Krebs\, Physics PhD Graduate
  Student
DESCRIPTION:Ballistic and hydrodynamic electron flow can develop in ma
 terials when carrier momentum is conserved over long distance and time
  scales. These non-Ohmic transport regimes are characterized by distin
 ctive spatial distributions of the current density and electrochemical
  potential. I will show scanning tunneling potentiometry (STP) measure
 ments of the electrochemical potential induced by DC transport in grap
 hene as a function of carrier density\, temperature\, and magnetic fie
 ld. First\, STP images are recorded as current flows through electrost
 atic constrictions with gate-tunable width that are "drawn" with the S
 TM tip. The electrochemical potential drop through these constrictions
  determines the wavevector-dependent conductivity σ(k) of the electro
 n fluid. Upon heating the system from 4.5 K to 77 K\, enhanced electro
 n-electron scattering leads to a crossover from ballistic to hydrodyna
 mic flow\, identified by super-ballistic conductance through the const
 rictions and a suppression of Landauer residual resistivity dipoles. W
 hen increasing the magnetic field from 0 to 1.4 T at 4.5 K\, the STP d
 ata reveals a diffusive-to-ballistic crossover in the flow of current 
 resulting from Landau level quantization. In the ballistic regime of m
 agnetotransport\, the local Hall field is enhanced one cyclotron diame
 ter away from scattering surfaces.
URL:https://www.physics.wisc.edu/events/?id=9206
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