Marginal Fermi Liquid in Twisted Bilayer Graphene.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Materials

Background:

• Linear resistivity at low temperatures is a key characteristic of high-temperature superconductors.
• This phenomenon has recently been observed in twisted bilayer graphene, prompting further investigation.
• Understanding the underlying mechanisms is crucial for advancing quantum materials research.

Purpose of the Study:

• To investigate the origin of T-linear resistivity in twisted bilayer graphene.
• To explore the connection between this behavior and the van Hove singularity (VHS).
• To identify the electronic properties and theoretical models that explain these observations.

Main Methods:

• Utilized a microscopic tight-binding model to simulate electronic properties.
• Analyzed the energy dependence of electron quasiparticle decay rates.
• Investigated low-temperature heat capacity and thermal conductivity.

Main Results:

• Demonstrated that an extended van Hove singularity (VHS) leads to T-linear resistivity near the singularity.
• Linked linear resistivity to a linear energy dependence of the quasiparticle decay rate, indicating marginal Fermi liquid behavior.
• Observed logarithmic corrections in heat capacity and thermal conductivity, violating the Wiedemann-Franz law.

Conclusions:

• The study confirms marginal Fermi liquid characteristics in twisted bilayer graphene due to an extended VHS.
• A crossover at approximately 6 Kelvin transitions to a regime dominated by Dirac cone excitations, also exhibiting linear resistivity.
• Findings align with experimental observations, providing a theoretical framework for understanding this quantum material's transport properties.