Correlated States in Triangular Moiré Superlattices
Dr. hab. Ipsita Mandal, prof. IFJ PAN

Date, Time
23.03, 15:00 - 16:00

Experiments on graphene bilayers, where the top layer is rotated with
respect to the one below, have displayed insulating behavior when the
moiré bands are partially filled. In the first part of the talk, I
will elaborate on our calculations to find the static charge
configurations in these phases, and to estimate the excitation gaps.
In the second part of the talk, I will focus on the properties of a
metal in a triangular lattice that undergoes a quantum phase
transition to a valley-polarized nematic state. Besides breaking the
threefold rotational symmetry of the triangular moiré superlattice,
this type of order also breaks twofold rotational and time-reversal
symmetries. At zero temperature, the ordered state displays a
pseudo-Goldstone mode due to the existence of a dangerously irrelevant
coupling λ in the 6-state clock model that describes the
valley-polarized nematic quantum critical point. Using a two-patch
model, we compute the fermionic self-energy to show that down to very
low energies, the Yukawa-like coupling between the pseudo-Goldstone
mode and the electronic degrees of freedom promotes the emergence of
non-Fermi liquid behavior. Below a crossover energy scale, Fermi
liquid behavior is recovered.