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Composite Fermi Liquid at Zero Magnetic Field in Twisted MoTe2 

Junkai Dong, Harvard University
Thursday, June 29, 2023 - 12:30pm to 1:30pm
PAB B421

The pursuit of exotic phases of matter outside of the extreme conditions of a quantizing magnetic field has been a longstanding quest of solid state physics. Recent experiments have observed spontaneous valley polarization and fractional Chern insulators (FCIs) in zero magnetic field in twisted bilayers of MoTe2, at partial filling of the topological valence band (ν=-2/3 and -3/5). We study the topological valence band at half filling, using exact diagonalization and density matrix renormalization group calculations. We discover a composite Fermi liquid (CFL) phase even at zero magnetic field that covers a large portion of the phase diagram centered around twist angle 3.6°. The CFL is a non-Fermi liquid phase that shows metallic behavior despite the absence of Landau quasiparticles. We discuss experimental implications including the competition between the CFL and a Fermi liquid, which can be tuned with a displacement field. The topological valence band has excellent quantum geometry over a wide range of twist angles and a small bandwidth that is, remarkably, reduced by interactions for a range of angles. These key properties are responsible for stabilizing the exotic quantum Hall phases we find at zero field. Finally, we present an optical signature  involving ``extinguished" optical responses as a means to identify Chern bands with ideal quantum geometry.

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