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CATEGORIES:Seminar
DESCRIPTION:Ancilla Theory of Mott Physics: from Cuprate to Twisted Bilayer
  Graphene\n\nI will introduce a new formalism to capture (partial) Mott loc
 alization in both the conventional Hubbard model and in topological flat ba
 nd relevant to  the twisted bilayer graphene (TBG).    I will first demonst
 rate that this framework reproduces the known results of the Mott insulator
 .  Then I will show two applications on more exotic  states which are chall
 enging to describe using conventional methods.  (1) In the context of high 
 Tc cuprate\, we can construct a fractional fermi liquid (FL*) phase  which 
 host both small hole pocket and localized  spin moments at filling n=1-p.  
 Our theory may provide an explanation of the ‘Fermi arcs’ observed in under
  doped cuprate\;  (2) In TBG\,  ancilla theory can capture Mott physics dir
 ectly in momentum space without the need of a lattice model with Wannier or
 bital.   In this language\, Mott gap is the hybridization gap between the p
 hysical band and an ancilla band.  In TBG\, the hybridization is equal to U
  at momentum away from Gamma\, but is constrained to have a node at Gamma p
 oint\, leading to a Mott semimetal instead of insulator at nu=0.  At nu=-1\
 , -2\, -3\, there is a transition from a correlated insulator to Mott semim
 etal upon decreasing interaction.   Most interestingly\, we propose a small
  Fermi surface pseudogap metal state at filling nu=-2-x\, which may be the 
 normal state of the superconductor.  At x=0 limit\, the quasiparticle is do
 minated by a composite polaron with vanishing overlap with physical electro
 n.  If time allowed\, I will also comment on the potential mechanism of sup
 erconductivity in this framework.
DTEND:20250429T172000Z
DTSTAMP:20260420T031551Z
DTSTART:20250429T162000Z
GEO:42.449741;-76.481209
LOCATION:Clark Hall\, 700
SEQUENCE:0
SUMMARY:Lassp and AEP Seminar: Yahui Zhang (Johns Hopkins University)
UID:tag:localist.com\,2008:EventInstance_49356929556181
URL:https://events.cornell.edu/event/lassp-and-aep-seminar-yahui-zhang-john
 s-hopkins-university-5160
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