Twist-angle-controlled anomalous gating in bilayer graphene/BN heterostructures

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Anomalous gating effects, including ineffective electrostatic control and resistance hysteresis, are observed in graphene encapsulated in boron nitride (BN).
• These effects are often linked to a potential ferroelectric state, but their origin, stability, and reproducibility are not well understood.
• Previous research has considered moiré superlattices formed between graphene and BN as a potential cause.

Purpose of the Study:

• To investigate the key parameter responsible for anomalous gating effects in graphene-boron nitride systems.
• To determine the role of angular alignment between BN layers versus graphene moiré superlattices.
• To establish reproducible conditions for observing these phenomena at room temperature.

Main Methods:

• Fabrication of dual-gated, dynamically rotatable van der Waals heterostructures using bilayer graphene encapsulated in BN.
• Systematic variation of the relative angular alignment between the two BN layers.
• Characterization of gating effects and resistance hysteresis at room temperature.

Main Results:

• The angular alignment between the two BN layers, not the graphene-BN moiré superlattice, is identified as the critical factor for anomalous gating.
• The anomalous gating effect is observed at room temperature for BN layer alignments between approximately 15° and 45°.
• Gate ineffectiveness and hysteresis exhibit high sensitivity to small angular changes, falling into three distinct regimes, with no evidence of a 60° periodicity.

Conclusions:

• The relative angular orientation of adjacent boron nitride layers is the primary determinant of anomalous gating effects in encapsulated graphene.
• Specific angular ranges (15°-45°) are identified as necessary for reproducible observation of these phenomena at room temperature.
• These findings provide crucial insights for controlling and investigating the microscopic origins of anomalous gating in 2D material heterostructures.