5 results on '"Kometter, Carlos R."'
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2. Mapping twist-tuned multiband topology in bilayer WSe2.
- Author
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Foutty, Benjamin A., Kometter, Carlos R., Devakul, Trithep, Reddy, Aidan P., Watanabe, Kenji, Taniguchi, Takashi, Fu, Liang, and Feldman, Benjamin E.
- Subjects
- *
SUPERLATTICES , *MAGNETIC insulators , *TOPOLOGY , *UNIT cell , *ELECTRONIC measurements - Abstract
Semiconductor moiré 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 moiré wavelengths, where interactions are most dominant. In this study, we conducted local electronic compressibility measurements of twisted bilayer WSe2 (tWSe2) at small twist angles. We demonstrated multiple topological bands that host a series of Chern insulators at zero magnetic field near a “magic angle” around 1.23°. Using a locally applied electric field, we induced a topological quantum-phase transition at one hole per moiré unit cell. Our work establishes the topological phase diagram of a generalized Kane-Mele-Hubbard model in tWSe2, demonstrating a tunable platform for strongly correlated topological phases. [ABSTRACT FROM AUTHOR]
- Published
- 2024
- Full Text
- View/download PDF
3. Hofstadter states and reentrant charge order in a semiconductor moir\'e lattice
- Author
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Kometter, Carlos R., Yu, Jiachen, Devakul, Trithep, Reddy, Aidan P., Zhang, Yang, Foutty, Benjamin A., Watanabe, Kenji, Taniguchi, Takashi, Fu, Liang, and Feldman, Benjamin E.
- Subjects
Condensed Matter - Mesoscale and Nanoscale Physics - Abstract
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$_2$/MoSe$_2$ 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.
- Published
- 2022
4. Robust fractional quantum Hall states and continuous quantum phase transitions in a half-filled bilayer graphene Landau level
- Author
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Zibrov, Alexander A., Kometter, Carlos. R., Zhou, Haoxin, Spanton, Eric M., Taniguchi, Takashi, Watanabe, Kenji, Zaletel, Michael P., and Young, Andrea F.
- Subjects
Condensed Matter - Strongly Correlated Electrons ,Condensed Matter - Materials Science ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed Matter - Mesoscale and Nanoscale Physics ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,Materials Science (cond-mat.mtrl-sci) ,FOS: Physical sciences - Abstract
Nonabelian anyons offer the prospect of storing quantum information in a topological qubit protected from decoherence, with the degree of protection determined by the energy gap separating the topological vacuum from its low lying excitations. Originally proposed to occur in quantum wells in high magnetic fields, experimental systems thought to harbor nonabelian anyons range from p-wave superfluids to superconducting systems with strong spin orbit coupling. However, all of these systems are characterized by small energy gaps, and despite several decades of experimental work, definitive evidence for nonabelian anyons remains elusive. Here, we report the observation of arobust, incompressible even-denominator fractional quantum Hall phase in a new generation of dual-gated, hexagonal boron nitride encapsulated bilayer graphene samples. Numerical simulations suggest that this state is in the Pfaffian phase and hosts nonabelian anyons, and the measured energy gaps are several times larger than those observed in other systems. Moreover, the unique electronic structure of bilayer graphene endows the electron system with two new control parameters. Magnetic field continuously tunes the effective electron interactions, changing the even-denominator gap non-monotonically and consistent with predictions that a transition between the Pfaffian phase and the composite Fermi liquid (CFL) occurs just beyond the experimentally explored magnetic field range. Electric field, meanwhile, tunes crossings between levels from different valleys. By directly measuring the valley polarization, we observe a continuous transition from an incompressible to a compressible phase at half-filling mediated by an unexpected incompressible, yet polarizable, intermediate phase. Valley conservation implies this phase is an electrical insulator with gapless neutral excitations., Considerably expanded and rewritten. New experimental data from two additional devices, including transport data and thermodynamic gap measurements up to 35T. Theoretical model updated to include screening from filled Landau levels. Experimental and numerical methods section greatly expanded. Paper, including Methods and supplementary data totals 27 pages with 20 figures, 3 tables
- Published
- 2016
5. Tunable spin and valley excitations of correlated insulators in Γ-valley moiré bands.
- Author
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Foutty BA, Yu J, Devakul T, Kometter CR, Zhang Y, Watanabe K, Taniguchi T, Fu L, and Feldman BE
- Abstract
Moiré superlattices formed from transition metal dichalcogenides support a variety of quantum electronic phases that are highly tunable using applied electromagnetic fields. While the valley degree of freedom affects optoelectronic properties in the constituent transition metal dichalcogenides, it has yet to be fully explored in moiré systems. Here we establish twisted double-bilayer WSe
2 as an experimental platform to study electronic correlations within Γ-valley moiré bands. Through local and global electronic compressibility measurements, we identify charge-ordered phases at multiple integer and fractional moiré fillings. By measuring the magnetic field dependence of their energy gaps and the chemical potential upon doping, we reveal spin-polarized ground states with spin-polaron quasiparticle excitations. In addition, an applied displacement field induces a metal-insulator transition driven by tuning between Γ- and K-valley moiré bands. Our results demonstrate control over the spin and valley character of the correlated ground and excited states in this system., (© 2023. The Author(s), under exclusive licence to Springer Nature Limited.)- Published
- 2023
- Full Text
- View/download PDF
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