Electronic nematic state and non-Fermi liquid transport phenomena in Magic Angle Twisted Bilayer Graphene: SU(4) valley + spin fluctuation Interference Mechanism

In the magic angle twisted bilayer graphene (MATBG), one of the most remarkable observations is the C3-symmetry-breaking nematic state. We identify that the nematicity in MATBG is the E-symmetry ferro bond order, which is the modulation of correlated hopping integrals owing to the E-symmetry particle-hole pairing condensation [1]. The nematicity in MATBG originates from prominent quantum interference among SU(4) valley+spin composite fluctuations. This novel "valley + spin fluctuation interference mechanism" is revealed by the density wave equation analysis for a realistic multiorbital Hubbard model for MATBG. We find that the nematic state is robust once three van Hove singularity points exist in each valley. This interference mechanism also causes novel time-reversal-symmetry-broken valley polarization accompanied by a charge loop current. We discuss interesting similarities and differences between MATBG and Fe-based superconductors. In addition, we study the no-Fermi liquid transport phenomena due to the SU(4) valley+spin composite fluctuations [2].

[1] S. Onari and H. Kontani, Phys. Rev. Lett. 128, 066401 (2022).

[2] D. Inoue, S. Onari and H. Kontani, unpublished.