Title: TBA

Abstract: TBA

Dr. Claudio Mazzoli, Brookhaven National Laboratory

Title: TBA

Abstract: TBA

Title: From Rhombohedral Graphene to Anomalous Hall Crystals

Abstract: Recent experiments on rhombohedral multilayer graphene (RMG) with a substrate-induced moire potential have identified both Chern insulators and fractional Quantum Hall states at zero magnetic field, whose origin is mysterious. The operative degrees of freedom are in the valence band minima that feature strong correlations and nontrivial quantum geometry. The first part of this talk will study a microscopic model of RMG. 

I will show that, even without a moire potential, interactions can spontaneously break continuous translation symmetry and time-reversal symmetry at the mean-field level to produce an electron crystal with finite Chern number. This new state of matter is called an anomalous Hall crystal. Many-body numerics at fractional fillings then reveal fractionalized ground states, consistent with experiments. I will show this result holds robustly for four-to-six layers for a range of displacement fields, and I will discuss the role of hBN alignment orientation. 

The second part of the talk will introduce λ-jellium, a minimal extension of the jellium model whose interaction strength and Berry curvature are independently tunable. I will show that it hosts an anomalous Hall crystal phase that is stable to quantum fluctuations with crystallization at much lower interaction strengths than in Wigner crystals.

Title: TBA

Abstract: TBA

Dr. Itamar Kimchi, Georgia Tech

Title: TBA

Abstract: TBA

Title: Quantum Twisting Microscopy of Moiré Flat Bands: A Theoretical Perspective

Abstract: Moiré materials with tunable flat bands provide an exceptional platform for realizing strongly correlated and topological phases. Achieving a detailed understanding of their electronic structure, however, remains a major challenge. The recently developed quantum twisting microscope introduces a new tunneling probe for van der Waals materials. In this talk, I will present a theoretical framework for both elastic and inelastic tunneling spectroscopy of moiré flat bands using the quantum twisting microscope. I will discuss how this technique can enable momentum-resolved measurements of electronic spectral functions, neutral collective excitations and superconducting gap structures in magic-angle twisted bilayer graphene.

Speaker: Dr. Xiaomeng Liu (Cornell)

Title: Superconductivity and Ferroelectric Orbital Magnetism in Semimetallic Rhombohedral Hexalayer Graphene

Abstract: Rhombohedral multilayer graphene has emerged as a promising platform for exploring correlated and topological quantum phases, enabled by its Berry-curvature-bearing flat bands. While prior work has focused on separated conduction and valence bands, we probe the semimetallic regime of rhombohedral hexalayer graphene. We uncovered a rich phase diagram dominated by flavor-symmetry breaking and an electric-field-driven band inversion. Near this inversion, we find a superconducting-like state confined to a region with emergent electron and hole Fermi surfaces. In addition, two multiferroic orbital-magnetic phases are observed: a ferrovalley state near zero field and a ferroelectric state at large fields around charge neutrality. The latter shows electric-field-reversible magnetic hysteresis, consistent with a multiferroic order parameter.

Title: Enhanced and Extended Strange Metallicity due to Coulomb Repulsion and Disorder

Abstract: I will discuss the problem of strange metals, where the traditional notion of Fermi liquid quasiparticles ceases to apply. I will view the problem through the lens of a model of electrons with Hubbard-U Coulomb repulsion and a disordered Yukawa coupling to a two-dimensional bosonic bath, which can be solved in an extended dynamical mean field theory scheme. The model exhibits a quantum critical point, at which the repulsive component of the electron interactions strongly enhances the effects of the quantum critical bosonic fluctuations on the electrons, leading to a breakdown of Fermi liquid physics and the formation of a strange metal with `Planckian' quasiparticle decay rates at low temperatures, although with no holographic dual. Furthermore, the eventual Mott transition that occurs as the repulsion is increased seemingly bounds the maximum decay rate in the strange metal. I will also discuss some applications and collaborations based on this work to the iron-based superconductors and moire materials. Time permitting, I will conclude with future directions to include nonlocal effects.  

Title: Strongly correlated topological phenomena in graphene multilayers

Abstract: Multilayer rhombohedral graphene has recently been experimentally demonstrated to host a panoply of strongly correlated and topological phenomena. In the presence of alignment to hBN, this platform exhibits Chern insulators and the fractional quantum anomalous Hall effect. On the other hand, signatures of unconventional (chiral) superconductivity arise in pristine multilayers. From a theoretical standpoint, several key issues are under active debate. In particular, what is the nature of the moire effect in this setting? How can we understand the emergence of these exotic topological states? I will discuss our progress towards resolving these questions, and highlight broader implications for other material platforms.