6 research outputs found
Mapping twist-tuned multi-band topology in bilayer WSe
Semiconductor moir\'e superlattices have been shown to host a wide array of
interaction-driven ground states. However, twisted homobilayers have been
difficult to study in the limit of large moir\'e wavelength, where interactions
are most dominant, and despite numerous predictions of nontrivial topology in
these homobilayers, experimental evidence has remained elusive. Here, we
conduct local electronic compressibility measurements of twisted bilayer
WSe at small twist angles. We demonstrate multiple topological bands which
host a series of Chern insulators at zero magnetic field near a 'magic angle'
around . Using a locally applied electric field, we induce a
topological quantum phase transition at one hole per moir\'e unit cell.
Furthermore, by measuring at a variety of local twist angles, we characterize
how the interacting ground states of the underlying honeycomb superlattice
depend on the size of the moir\'e unit cell. Our work establishes the
topological phase diagram of a generalized Kane-Mele-Hubbard model in tWSe,
demonstrating a tunable platform for strongly correlated topological phases
Tunable spin and valley excitations of correlated insulators in -valley moir\'e bands
Moir\'e superlattices formed from transition metal dichalcogenides (TMDs)
have been shown to support a variety of quantum electronic phases that are
highly tunable using applied electromagnetic fields. While the valley character
of the low-energy states dramatically affects optoelectronic properties in the
constituent TMDs, this degree of freedom has yet to be fully explored in
moir\'e systems. Here, we establish twisted double bilayer WSe as an
experimental platform to study electronic correlations within -valley
moir\'e bands. Through a combination of local and global electronic
compressibility measurements, we identify charge-ordered phases at multiple
integer and fractional moir\'e band fillings . By measuring the magnetic
field dependence of their energy gaps and the chemical potential upon doping,
we reveal spin-polarized ground states with novel spin polaron quasiparticle
excitations. In addition, an applied displacement field allows us to realize a
new mechanism of metal-insulator transition at driven by tuning
between - and -valley moir\'e bands. Together, our results
demonstrate control over both the spin and valley character of the correlated
ground and excited states in this system
Hofstadter states and reentrant charge order in a semiconductor moir\'e lattice
The emergence of moir\'e materials with flat bands provides a platform to
systematically investigate and precisely control correlated electronic phases.
Here, we report local electronic compressibility measurements of a twisted
WSe/MoSe heterobilayer which reveal a rich phase diagram of
interpenetrating Hofstadter states and electron solids. We show that this
reflects the presence of both flat and dispersive moir\'e bands whose relative
energies, and therefore occupations, are tuned by density and magnetic field.
At low densities, competition between moir\'e bands leads to a transition from
commensurate arrangements of singlets at doubly occupied sites to triplet
configurations at high fields. Hofstadter states (i.e., Chern insulators) are
generally favored at high densities as dispersive bands are populated, but are
suppressed by an intervening region of reentrant charge-ordered states in which
holes originating from multiple bands cooperatively crystallize. Our results
reveal the key microscopic ingredients that favor distinct correlated ground
states in semiconductor moir\'e systems, and they demonstrate an emergent
lattice model system in which both interactions and band dispersion can be
experimentally controlled
Harnessing excitons at the nanoscale -- photoelectrical platform for quantitative sensing and imaging
Excitons -- quasiparticles formed by the binding of an electron and a hole
through electrostatic attraction -- hold promise in the fields of quantum light
confinement and optoelectronic sensing. Atomically thin transition metal
dichalcogenides (TMDs) provide a versatile platform for hosting and
manipulating excitons, given their robust Coulomb interactions and exceptional
sensitivity to dielectric environments. In this study, we introduce a cryogenic
scanning probe photoelectrical sensing platform, termed exciton-resonant
microwave impedance microscopy (ER-MIM). ER-MIM enables ultra-sensitive probing
of exciton polarons and their Rydberg states at the nanoscale. Utilizing this
technique, we explore the interplay between excitons and material properties,
including carrier density, in-plane electric field, and dielectric screening.
Furthermore, we employ deep learning for automated data analysis and
quantitative extraction of electrical information, unveiling the potential of
exciton-assisted nano-electrometry. Our findings establish an invaluable
sensing platform and readout mechanism, advancing our understanding of exciton
excitations and their applications in the quantum realm
Emergent Dirac gullies and gully-symmetry breaking quantum Hall states in ABA trilayer graphene
We report on quantum capacitance measurements of high quality, graphite- and
hexagonal boron nitride encapsulated Bernal stacked trilayer graphene devices.
At zero applied magnetic field, we observe a number of electron density- and
electrical displacement-tuned features in the electronic compressibility
associated with changes in Fermi surface topology. At high displacement field
and low density, strong trigonal warping gives rise to emergent Dirac gullies
centered near the corners of the hexagonal Brillouin and related by three fold
rotation symmetry. At low magnetic fields of ~T, the gullies manifest
as a change in the degeneracy of the Landau levels from two to three. Weak
incompressible states are also observed at integer filling within these
triplets Landau levels, which a Hartree-Fock analysis indicates are associated
with Coulomb-driven nematic phases that spontaneously break rotation symmetry.Comment: Main text: 5 pages, 3 Figures. Supplements: 8 pages, 5 figure