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Ronen, Yuval

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Ronen

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Yuval

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Ronen, Yuval

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2020 - 20212

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Author's Publications: search.filters.isAuthorOfPublication.424a647a-403f-4b94-8927-5f980b33435a

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    Tunable spin-polarized correlated states in twisted double bilayer graphene
    (Springer Science and Business Media LLC, 2020-07-08) Liu, Xiaomeng; Hao, Zeyu; Khalaf, Eslam; Lee, Jong Yeon; Ronen, Yuval; Yoo, Hyobin; Haei Najafabadi, Danial; Watanabe, Kenji; Taniguchi, Takashi; Vishwanath, Ashvin; Kim, Philip
    Reducing the energy bandwidth of electrons in a lattice below the long-range Coulomb interaction energy promotes correlation effects. Created by stacking van der Waals (vdW) heterostructures with a controlled twist angle1–3, moire ́ superlattices enable the engineering of electron band structure. In an engineered moire ́ flat band, exotic quantum phases can emerge. The correlated insulator, superconductivity, and quantum anomalous Hall ef- fect found in the flat band of the magic angle twisted bilayer graphene (MA-TBG) 4–8 have sparkled exploration of correlated electron states in other moire ́ systems 9–11. The electronic properties of vdW moire ́ superlattices can further be tuned by adjusting the interlayer cou- pling 6 or the band structure of constituent layers 9. Here, employing vdW heterostructures of twisted double bilayer graphene (TDBG), we demonstrate a flat electron band that is tun- able by perpendicular electric fields in a range of twist angles. Similar to the MA-TBG, TDBG exhibits energy gaps at the half- and quarter-filled flat bands, indicating the emergence of correlated insulating states. We find that the gaps of these insulating states increase with in-plane magnetic field, suggesting a ferromagnetic order. Upon doping the half-filled insulator, a sudden drop of resistivity is observed with lowering temperature. This critical behavior is confined in a small area in the density-electric field plane, and is attributed to a phase transition from a normal metal to a spin-polarized correlated state. Spin-polarized correlated states discovered in the electric field tunable TDBG provide a new route to engineering interaction-driven quantum phases.
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    Aharonov-Bohm Effect in Graphene-Based Fabry-Pérot Quantum Hall Interferometers
    (Springer Nature, 2021-02-25) Ronen, Yuval; Werkmeister, Thomas; Najafabadi, Danial; Pierce, Andrew; Anderson, Laurel; Shin, Young Jae; Lee, Si Young; Lee, Young Hee; Johnson, Bobae; Watanabe, Kenji; Taniguchi, Takashi; Yacoby, Amir; Kim, Philip
    Interferometers probe the wave-nature and exchange statistics of indistinguishable particles, for example electrons in the chiral one-dimensional edge channels of the quantum Hall effect (QHE). Quantum point contacts can split and recombine these channels, enabling interference of charged particles. Such quantum Hall interferometers (QHIs) can unveil the exchange statistics of anyonic quasiparticles in the fractional quantum Hall effect (FQHE). Here, we present a fabrication technique for QHIs in van der Waals (vdW) materials and realize a tunable, graphene-based Fabry-Pérot (FP) QHI. The graphite encapsulated architecture allows observation of FQHE at 3T magnetic field and precise partitioning of integer and fractional edge modes. We measure pure Aharonov-Bohm interference in the integer QHE, a major technical challenge in small FP interferometers, and find that edge modes exhibit high visibility interference due to large velocities. Our results establish vdW heterostructures as a versatile alternative to GaAs-based interferometers for future experiments targeting anyonic quasiparticles.