Negative differential resistance of viscous electron flow in graphene

Abstract Negative differential resistance (NDR) devices show a decrease in the voltage drop with increasing current, an advantageous feature for amplifying and oscillating circuits. We introduce a NDR mechanism based on the electron hydrodynamics of two dimensional (2D) materials. An increase of the current in the system favors electron-electron collisions so that a ballistic-hydrodynamic transition takes place and the device resistance is reduced. This phenomenon results in NDR provided that the electron’s mean free path is much longer than the device size. We discuss the strategies towards NDR and find that geometrically engineered devices make it possible to achieve NDR in graphene with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:mo>∼</mml:mo> </mml:mrow> <mml:mn>200</mml:mn> <mml:mstyle scriptlevel="0"/> <mml:mtext>nm</mml:mtext> </mml:mrow> </mml:math> sized geometrical features. This NDR mechanism is revealed as a new hydrodynamic signature, particularly relevant in graphene devices for 2D electronics and high-frequency operation.