Three-Carrier Spin Blockade and Coupling in Bilayer Graphene Double Quantum Dots

Area of Science:

• Condensed matter physics
• Quantum information science
• Spintronics

Background:

• Spin degrees of freedom are fundamental to condensed matter systems.
• Spin-mixing mechanisms are crucial for controlling spin qubits and understanding material properties.
• Bilayer graphene quantum dots exhibit long spin-relaxation times (T1 up to 50 ms) with magnetic field dependence.

Purpose of the Study:

• Investigate spin-blockade phenomena in bilayer graphene quantum dots at the (1,2)↔(0,3) charge configuration.
• Examine the influence of interdot tunnel coupling and external magnetic field orientation on spin-blockade leakage current.
• Elucidate the underlying spin-mixing mechanisms in these systems.

Main Methods:

• Fabrication and characterization of electrostatically defined bilayer graphene quantum dots.
• Measurement of spin-blockade leakage current as a function of interdot tunnel coupling.
• Systematic variation of the magnitude and orientation of applied magnetic fields (in-plane and out-of-plane).

Main Results:

• Observed a zero-field current peak in out-of-plane magnetic field, potentially due to cotunneling, with side peaks suggesting additional spin- and valley-mixing.
• Detected a zero-field current dip in in-plane magnetic field, attributed to competition between spin Zeeman effect and Kane-Mele spin-orbit interaction.
• Line shape analysis of the current dip indicates the involvement of further complex mechanisms.

Conclusions:

• Spin-blockade phenomena in bilayer graphene quantum dots are sensitive to magnetic field orientation and coupling strengths.
• Multiple spin-mixing mechanisms, including spin-orbit interactions, contribute to the observed transport characteristics.
• Further investigation is needed to fully understand the intricate spin dynamics and identify all contributing mechanisms.