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Ballistic Electron Source with Magnetically Controlled Valley Polarization in Bilayer Graphene
Josep Ingla-Aynés1, Antonio L R Manesco1, Talieh S Ghiasi1
1Kavli Institute of Nanoscience, <a href="https://ror.org/02e2c7k09">Delft University of Technology</a>, Lorentzweg 1, 2628 CJ Delft, The Netherlands.
Researchers achieved tunable valley polarization in bilayer graphene using quantum point contacts and magnetic fields. This breakthrough enables precise control over electron currents for future valleytronic devices.
Area of Science:
- Condensed Matter Physics
- Materials Science
- Nanotechnology
Background:
- Valleytronics offers a promising avenue for next-generation electronic devices.
- Controlling valley-polarized electron currents is crucial for realizing valleytronic functionalities.
- Bilayer graphene (BLG) presents a unique platform for exploring valleytronics due to its electronic properties.
Purpose of the Study:
- To investigate the generation and control of valley-polarized electron currents in bilayer graphene.
- To demonstrate the feasibility of using quantum point contacts (QPCs) and magnetic fields for valley manipulation.
- To explore the robustness and tunability of valley polarization effects in BLG.
Main Methods:
- Ballistic coherent transport experiments in a BLG channel defined by electrostatic gating.
- Utilizing two opposite quantum point contacts (QPCs) to define electron pathways.
- Applying an out-of-plane magnetic field to steer electron currents.
- Tuning carrier density and QPC modes via gate voltage.
- Employing semiclassical simulations to validate experimental observations.
Main Results:
- Observation of two distinct current jets resulting from valley-dependent trigonal warping.
- Confirmation that these current jets exhibit opposite valley polarization.
- Demonstration of the effect's robustness across a range of QPC modes (m=1 to m=6).
- Successful quantitative reproduction of jet separations using semiclassical simulations without fitting parameters.
- Achieved full control over the valley polarization of collected currents by steering individual jets.
Conclusions:
- Ballistic transport in BLG with QPCs and magnetic fields allows for precise control of valley polarization.
- The observed current jets are a direct consequence of valley-dependent trigonal warping in BLG.
- This work establishes a foundation for developing ballistic current sources with tunable valley polarization for advanced electronic applications.
- Collimation experiments serve as a sensitive method for probing Fermi surface properties like trigonal warping.
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