Giant Second-Order Nonlinear Hall Effect in Twisted Bilayer Graphene.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid State Physics

Background:

• The nonlinear Hall effect (NLHE) can arise without breaking time-reversal symmetry, requiring only inversion symmetry breaking.
• Disorder-induced contributions are significant in NLHE, yet experimental studies on their specific roles are limited.
• Understanding disorder mechanisms is crucial for harnessing NLHE in electronic devices.

Purpose of the Study:

• To investigate the dominant mechanisms behind the giant nonlinear response in twisted bilayer graphene.
• To explore the tunability of the second-order nonlinearity by gate voltage.
• To elucidate the interplay between static (impurities) and dynamic (phonons) disorders in NLHE.

Main Methods:

• Fabrication and characterization of twisted bilayer graphene devices.
• Electrical transport measurements to probe the nonlinear Hall effect.
• Temperature-dependent measurements to distinguish between impurity and phonon contributions.

Main Results:

• A giant second-order nonlinear Hall response was observed in twisted bilayer graphene, significantly exceeding intrinsic contributions in materials like WTe2.
• The magnitude and sign of the nonlinearity were effectively controlled by gate voltage.
• Disorder-induced skew scattering, a combination of static impurity and dynamic phonon scattering, was identified as the primary source of the giant NLHE.

Conclusions:

• Twisted bilayer graphene exhibits a colossal disorder-dominated nonlinear Hall effect.
• Both static and dynamic disorders play collaborative roles, with impurity skew scattering dominant at low temperatures and phonon skew scattering becoming comparable at higher temperatures.
• This study provides a comprehensive experimental understanding of disorder mechanisms in NLHE, paving the way for novel electronic applications.