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Quantum oscillations probe the Fermi surface topology of the nodal-line semimetal CaAgAs
Nodal semimetals are a unique platform to explore topological signatures of the unusual band structure that can manifest by accumulating a nontrivial phase in quantum oscillations. Here we report a…
Domain wall competition in the Chern insulating regime of twisted bilayer graphene
- Y. H. Kwan, Glenn Wagner, N. Chakraborty, S. Simon, S. Parameswaran
- Physics, Materials SciencePhysical Review B
- 15 July 2020
We consider magic-angle twisted bilayer graphene (TBG) at filling $\nu=+3$, where experiments have observed a robust quantized anomalous Hall effect. This has been attributed to the formation of a…
Twisted bilayer graphene in a parallel magnetic field
We study the effect of an in-plane magnetic field on the noninteracting dispersion of twisted bilayer graphene. Our analysis is rooted in the chirally symmetric continuum model, whose zero-field band…
Kekulé Spiral Order at All Nonzero Integer Fillings in Twisted Bilayer Graphene
Y.H. Kwan, G. Wagner, T. Soejima, M.P. Zaletel, 3 S.H. Simon, S.A. Parameswaran, and N. Bultinck 4 Rudolf Peierls Centre for Theoretical Physics, University of Oxford, Oxford OX1 3PU, United Kingdom…
Theory of competing excitonic orders in insulating WTe2 monolayers
We develop a theory of the excitonic phase recently proposed as the zero-field insulating state observed near charge neutrality in monolayer WTe$_2$. Using a Hartree-Fock approximation, we…
Excitonic fractional quantum Hall hierarchy in Moiré heterostructures
We consider fractional quantum Hall states in systems where two flat Chern number $C=\pm 1$ bands are labeled by an approximately conserved 'valley' index and interchanged by time reversal symmetry.…
Exciton Band Topology in Spontaneous Quantum Anomalous Hall Insulators: Applications to Twisted Bilayer Graphene.
- Y. H. Kwan, Yichen Hu, S. Simon, S. Parameswaran
- Medicine, PhysicsPhysical review letters
- 25 March 2020
Using an exactly solvable model, topological features of neutral particle-hole pair excitations of correlated quantum anomalous Hall (QAH) insulators are uncovered whose approximately flat conduction and valence bands have equal and opposite nonzero Chern number.
Quantum oscillations in the zeroth Landau Level and the serpentine Landau fan
We identify an unusual mechanism for quantum oscillations in nodal semimetals, driven by a single pair of Landau levels periodically closing their gap at the Fermi energy as a magnetic field is…
Global phase diagram of twisted bilayer graphene above $T_c$
We investigate the full doping and strain-dependent phase diagram (absent superconductivity) of magic-angle twisted bilayer graphene (TBG). Using comprehensive Hartree-Fock calculations, we show that…
Quantum Oscillations in the Zeroth Landau Level: Serpentine Landau Fan and the Chiral Anomaly.
This work links the Landau spectrum of a two-dimensional (2D) nodal semimetal to the Rabi model, and shows by exact solution that, across the entire Landau fan, pairs of opposite-parity Landau levels are intertwined in a "serpentine" manner.