When: October 4th at 11am Where: ATL 4402 Speaker: Dr. Yahui Zhang Title: Exotic exciton phases and quantum spin liquids in quantum Hall bilayer and moire bilayer Abstract: In this talk I will discuss some exotic phases of excitons beyond the conventional exciton condensation phase. (1) In the first part, I will consider a coulomb coupled quantum Hall bilayer at filling (1/3,-1/3). (Equivalently (1/3,2/3)) and then tune d/l_b. d is inter-layer distance and l_B is magnetic length. I propose that there is a continuous quantum phase transition between an exciton condensation phase at small d and the decoupled Laughlin state at large d. The transition is driven by condensation of a fractional exciton formed by anyone with 1/3 and -1/3 charges in the two layers. This critical point is in the universality class of XY*. (2) In the second part, I consider a moire bilayer and use the layer pseudo-spin to simulate spin physics. “Magnon” of this pseudo spin is just the inter-layer exciton discussed in the first part. Similar to quantum Hall bilayer, conductivity of this pseudo-spin can be electrically measured through the counter-flow techniques. Thus one may obtain smoking gun evidences of certain quantum spin liquids. I will provide some examples of quantum spin liquids which may be realized in this system, including chiral spin liquid, Z2 spin liquid and spinon Fermi surface.