5 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
Spin skyrmion gaps as signatures of strong-coupling insulators in magic-angle twisted bilayer graphene
The flat electronic bands in magic-angle twisted bilayer graphene (MATBG)
host a variety of correlated insulating ground states, many of which are
predicted to support charged excitations with topologically non-trivial spin
and/or valley skyrmion textures. However, it has remained challenging to
experimentally address their ground state order and excitations, both because
some of the proposed states do not couple directly to experimental probes, and
because they are highly sensitive to spatial inhomogeneities in real samples.
Here, using a scanning single-electron transistor, we observe thermodynamic
gaps at even integer moir\'e filling factors at low magnetic fields. We find
evidence of a field-tuned crossover from charged spin skyrmions to bare
particle-like excitations, suggesting that the underlying ground state belongs
to the manifold of strong-coupling insulators. From the spatial dependence of
these states and the chemical potential variation within the flat bands, we
infer a link between the stability of the correlated ground states and local
twist angle and strain. Our work advances the microscopic understanding of the
correlated insulators in MATBG and their unconventional excitations.Comment: Supplementary information available at
https://www.nature.com/articles/s41467-023-42275-
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
Data for "Spin skyrmion gaps as signatures of strong-coupling insulators in magic-angle twisted bilayer graphene"
This is the experimental data for the paper "Spin skyrmion gaps as signatures of strong-coupling insulators in magic-angle twisted bilayer graphene", to appear in Nature Communications