Person: Jarillo-Herrero, Pablo
Loading...
Email Address
AA Acceptance Date
Birth Date
Research Projects
Organizational Units
Job Title
Last Name
Jarillo-Herrero
First Name
Pablo
Name
Jarillo-Herrero, Pablo
5 results
Search Results
Now showing 1 - 5 of 5
Publication Observation of Interband Collective Excitations in Twisted Bilayer Graphene(Springer Science and Business Media LLC, 2021-09-27) Hesp, Niels C. H.; Torre, Iacopo; Rodan Legrain, Daniel; Novelli, Pietro; Cao, Yuan; Carr, Stephen; Fang, Shiang; Stepanov, Petr; Barcons-Ruiz, David; Herzig Sheinfux, Hanan; Watanabe, Kenji; Taniguchi, Takashi; Efetov, Dmitri K.; Kaxiras, Efthimios; Jarillo-Herrero, Pablo; Polini, Marco; Koppens, Frank H. L.The single-particle and many-body properties of twisted bilayer graphene (TBG) can be dramatically 1 different from those of a single graphene layer, in particular when the two layers are rotated relative 2 to each other by a small angle ��≈��∘1–6. Here, we probe for the first time collective excitations of TBG 3 graphene with 20 nanometer spatial resolution, by applying mid-infrared (MIR) near-field optical 4 microscopy. We unveil a propagating plasmon mode in charge-neutral TBG with ��=��.��−��.��∘, which 5 is dramatically different from the ordinary single-layer graphene intraband plasmon7,8. We interpret it 6 as an interband plasmon associated with the optical transitions between minibands originating from 7 the moiré superlattice9,10. The details of the plasmon dispersion are directly related to the motion of 8 electrons in the moiré superlattice and offer invaluable insight into a plethora of physical properties, 9 such as the band nesting between flat band and remote band10, local interlayer coupling, losses etc. We 10 find a strongly reduced interlayer coupling in the regions with AA-stacking, pointing at screening due 11 to electron-electron (e-e) interactions. Optical nano-imaging studies of TBG pave the way to spatially 12 probe interactions effects at the nanoscale11, it could potentially elucidate the contribution of collective excitations to many-body ground states12, and it unveils itself as a new platform for strong light-matter 14 interactions and quantum plasmonic studies and devices13.Publication Enhancement of Interlayer Exchange in an Ultrathin Two-Dimensional Magnet(Springer Science and Business Media LLC, 2019-09-16) Klein, Dahlia; MacNeill, David; Song, Qian; Larson, Daniel; Fang, Shiang; Xu, Mingyu; Ribeiro, R. A.; Canfield, P. C.; Kaxiras, Efthimios; Comin, Riccardo; Jarillo-Herrero, PabloFollowing the recent isolation of monolayer CrI3 [1], there has been a surge of new two-dimensional van der Waals magnetic materials [2-12], whose incorporation in van der Waals heterostructures offers a new platform for spintronics [5-9], proximity magnetism [13], and quantum spin liquids [14]. A primary question in this burgeoning field is how exfoliating crystals to the few-layer limit influences their magnetism. Studies on CrI3 have shown a different magnetic ground state for ultrathin exfoliated films [1,5,6] but the origin is not yet understood. Here, we use electron tunneling through few-layer crystals of the layered antiferromagnetic insulator CrCl3 to probe its magnetic order, finding a ten-fold enhancement in the interlayer exchange compared to bulk crystals. Moreover, temperature- and polarization-dependent Raman spectroscopy reveal that the crystallographic phase transition of bulk crystals does not occur in exfoliated films. This results in a different low temperature stacking order and, we hypothesize, increased interlayer exchange. Our study provides new insight into the connection between stacking order and interlayer interactions in novel two-dimensional magnets, which may be relevant for correlating stacking faults and mechanical deformations with the magnetic ground states of other more exotic layered magnets, such as RuCl3 [14].Publication Fractional Chern Insulators in Magic-Angle Twisted Bilayer Graphene(Springer Science and Business Media LLC, 2021-12-15) Xie, Yonglong; Pierce, Andrew; Park, Jeong Min; Parker, Daniel E.; Khalaf, Eslam; Ledwith, Patrick; Cao, Yuan; Lee, Seung Hwan; Chen, Shaowen; Forrester, Patrick R.; Watanabe, Kenji; Taniguchi, Takashi; Vishwanath, Ashvin; Jarillo-Herrero, Pablo; Yacoby, AmirAbstractFractional Chern insulators (FCIs) are lattice analogues of fractional quantum Hall states that may provide a new avenue towards manipulating non-Abelian excitations. Early theoretical studies1–7 have predicted their existence in systems with flat Chern bands and highlighted the critical role of a particular quantum geometry. However, FCI states have been observed only in Bernal-stacked bilayer graphene (BLG) aligned with hexagonal boron nitride (hBN)8, in which a very large magnetic field is responsible for the existence of the Chern bands, precluding the realization of FCIs at zero field. By contrast, magic-angle twisted BLG9–12 supports flat Chern bands at zero magnetic field13–17, and therefore offers a promising route towards stabilizing zero-field FCIs. Here we report the observation of eight FCI states at low magnetic field in magic-angle twisted BLG enabled by high-resolution local compressibility measurements. The first of these states emerge at 5 T, and their appearance is accompanied by the simultaneous disappearance of nearby topologically trivial charge density wave states. We demonstrate that, unlike the case of the BLG/hBN platform, the principal role of the weak magnetic field is merely to redistribute the Berry curvature of the native Chern bands and thereby realize a quantum geometry favourable for the emergence of FCIs. Our findings strongly suggest that FCIs may be realized at zero magnetic field and pave the way for the exploration and manipulation of anyonic excitations in flat moiré Chern bands.Publication Observation of Electron Coherence and Fabry–Perot Standing Waves at a Graphene Edge(American Chemical Society (ACS), 2017-11-08) Allen, Monica; Shtanko, Oles; Fulga, Ion; Wang, Joel; Nurgaliev, Daniyar; Watanabe, Kenji; Taniguchi, Takashi; Akhmerov, Anton; Jarillo-Herrero, Pablo; Levitov, Leonid; Yacoby, AmirElectron surface states in solids are typically confined to the outermost atomic layers and, due to surface disorder, have negligible impact on electronic transport. Here, we demonstrate a very different behavior for surface states in graphene. We probe the wavelike character of these states by Fabry–Perot (FP) interferometry and find that, in contrast to theoretical predictions, these states can propagate ballistically over micron-scale distances. This is achieved by embedding a graphene resonator formed by gate-defined p–n junctions within a graphene superconductor–normal–superconductor structure. By combining superconducting Aharanov–Bohm interferometry with Fourier methods, we visualize spatially resolved current flow and image FP resonances due to p–n–p cavity modes. The coherence of the standing-wave edge states is revealed by observing a new family of FP resonances, which coexist with the bulk resonances. The edge resonances have periodicity distinct from that of the bulk states manifest in a repeated spatial redistribution of current on and off the FP resonances. This behavior is accompanied by a modulation of the multiple Andreev reflection amplitude on-and-off resonance, indicating that electrons propagate ballistically in a fully coherent fashion. These results, which were not anticipated by theory, provide a practical route to developing electron analog of optical FP resonators at the graphene edge.Publication Enhancement of Interlayer Exchange in an Ultrathin Two-Dimensional Magnet(Springer Science and Business Media LLC, 2019-09-16) Song, Qian; Fang, Shiang; Xu, Mingyu; Ribeiro, R. A.; Canfield, P. C.; Kaxiras, Efthimios; Comin, Riccardo; Jarillo-Herrero, Pablo; Klein, Dahlia; MacNeill, David; Larson, Daniel; Canfield, PFollowing the recent isolation of monolayer CrI3, many more two-dimensional van der Waals magnetic materials have been isolated. Their incorporation in van der Waals heterostructures offers a new platform for spintronics proximity magnetism and quantum spin liquids. A primary question in this field is how exfoliating crystals to the few-layer limit influences their magnetism. Studies of CrI3 have shown a different magnetic ground state for ultrathin exfoliated films compared with the bulk, but the origin is not yet understood. Here, we use electron tunnelling through few-layer crystals of the layered antiferromagnetic insulator CrCl3 to probe its magnetic order and find a tenfold enhancement of the interlayer exchange compared with bulk crystals. Moreover, temperature- and polarization-dependent Raman spectroscopy reveals that the crystallographic phase transition of bulk crystals does not occur in exfoliated films. This results in a different low-temperature stacking order and, we hypothesize, increased interlayer exchange. Our study provides insight into the connection between stacking order and interlayer interactions in two-dimensional magnets, which may be relevant for correlating stacking faults and mechanical deformations with the magnetic ground states of other more exotic layered magnets such as RuCl3.