Speaker (1):         Michael Peterson ?" CSU Long Beach

Title:               Exact Diagonalization studies of Abelian and non-Abelian States in 2/3-filled Bilayer Fractional Quantum Hall Systems               

Abstract:        I will discuss recent numerical exact diagonalization results investigating the quantum phase diagram of the 2/3-filled bilayer fractional quantum Hall effect as a function of interlayer separation and tunneling.   In particular, I will address the competition and quantum phase transitions between possible abelian states (the Halperin 330, particle-hole conjugate 2/3 Laughlin, and pseudo-spin singlet states) and the Z4 parafermion non-abelian state.

Speaker (2):         Yang-Le Wu ?" University of Maryland

Title:               Monte Carlo energetics of ? = 2/3 quantum Hall bilayers

Abstract:        The possibility to stabilize exotic topological phases in fractional quantum Hall bilayers is a subject of strong current interest. The bilayer system provides a rich set of tunable parameters, and it may host a variety of Abelian and non-Abelian phases at total filling ? = 2/3. In this talk, I will present some recent numerical results obtained from variational Monte Carlo calculations. I will discuss the phase diagram in the lowest and the second Landau levels, as well as the effect of tuning the interlayer repulsion slightly away from the Coulomb point.

Speaker (3):         Mike Zaletel ?" Station Q

Title:                Numerical evidence for spin-charge separated non-Abelions in nu = 1/3 + 1/3 quantum Hall bilayers

Abstract:        Quantum Hall systems with internal degrees of freedom such as spin, valley, or bilayer index provide a unique opportunity to experimentally tune between competing  topologically ordered phases at the same filling factor. Here we study two-component ‘bilayer’  systems in which one can experimentally tune the single-particle tunneling and interaction strength between two spatially separated 2DEGs. At filling nu = 1/3 + 1/3 a variety of exotic non-Abelian phases have been proposed, such as emergent Fibonacci anyons and Z4 parafermions. We study the problem  using the infinite density matrix renormalization group. In the simplest experimentally relevant phase diagram, we find three Abelian phases that meet at a triple point. Adding small perturbations to the inter-layer interaction, which might be introduced by complications like Landau-level and sub-band mixing, drives the system into a non-Abelian phase we tentatively identify as the `inter-layer Pfaffian.’ I will focus on the theoretical structure of pseudospin-charge separation in this phase and how it can be reliably detected in numerics. If time permits, I’ll also show some pictures of Fibonacci anyons  found using Coulomb interactions at nu = 12/5.