Specular Electron Focusing between Gate-Defined Quantum Point Contacts in Bilayer Graphene

Area of Science:

• Condensed matter physics
• Materials science
• Quantum electronics

Background:

• Bilayer graphene (BLG) exhibits unique electronic properties due to its layered structure.
• Quantum point contacts (QPCs) are essential for controlling and probing electron transport in nanoscale devices.
• Understanding electron behavior in ballistic channels is key for future electronic applications.

Purpose of the Study:

• To investigate the effects of size quantization and trigonal warping on transverse electron focusing (TEF) in BLG.
• To analyze electron reflection properties at gate-defined edges in a ballistic BLG channel.
• To explore the potential of BLG for novel electronic and valleytronic devices.

Main Methods:

• Fabrication of a multiterminal ballistic bilayer graphene channel.
• Utilizing electrostatic gating to define multiple spin- and valley-degenerate quantum point contacts (QPCs).
• Performing transverse electron focusing (TEF) measurements with varying QPC geometries and crystallographic orientations.

Main Results:

• Observed eight clear peaks in TEF spectra with comparable amplitudes, indicating specular electron reflections.
• Demonstrated phase-coherent transport and weak quantum interference signatures at low temperatures.
• Showcased the visibility of TEF peaks up to 100 K, despite small gate-induced bandgaps (≲45 meV).

Conclusions:

• Specular reflection at gate-defined edges preserves pseudospin information, crucial for valleytronics.
• Ballistic transport in BLG channels is achievable and robust over a range of temperatures.
• The results pave the way for realizing ballistic interconnects in next-generation valleytronic devices.