8 research outputs found
Signatures of Z Vestigial Potts-nematic order in van der Waals antiferromagnets
Layered van der Waals magnets have attracted much recent attention as a
promising and versatile platform for exploring intrinsic two-dimensional
magnetism. Within this broader class, the transition metal phosphorous
trichalcogenides P stand out as particularly interesting, as they
provide a realization of honeycomb lattice magnetism and are known to display a
variety of magnetic ordering phenomena as well as superconductivity under
pressure. One example, found in a number of different materials, is
commensurate single- zigzag antiferromagnetic order, which spontaneously
breaks the spatial threefold rotation symmetry of the honeycomb
lattice. The breaking of multiple distinct symmetries in the magnetic phase
suggests the possibility of a sequence of distinct transitions as a function of
temperature, and a resulting intermediate -nematic phase which
exists as a paramagnetic vestige of zigzag magnetic order -- a scenario known
as vestigial ordering. Here, we report the observation of key signatures of
vestigial Potts-nematic order in rhombohedral FePSe. By performing linear
dichroism imaging measurements -- an ideal probe of rotational symmetry
breaking -- we find that the symmetry is already broken above the N\'eel
temperature. We show that these observations are explained by a general
Ginzburg-Landau model of vestigial nematic order driven by magnetic
fluctuations and coupled to residual strain. An analysis of the domain
structure as temperature is lowered and a comparison with zigzag-ordered
monoclinic FePS reveals a broader applicability of the Ginzburg-Landau
model in the presence of external strain, and firmly establishes the P
magnets as a new experimental venue for studying the interplay between
Potts-nematicity, magnetism and superconductivity.Comment: 6 pages, 4 figures + supplementary materia
Charge-transfer Contact to a High-Mobility Monolayer Semiconductor
Two-dimensional (2D) semiconductors, such as the transition metal
dichalcogenides, have demonstrated tremendous promise for the development of
highly tunable quantum devices. Realizing this potential requires
low-resistance electrical contacts that perform well at low temperatures and
low densities where quantum properties are relevant. Here we present a new
device architecture for 2D semiconductors that utilizes a charge-transfer layer
to achieve large hole doping in the contact region, and implement this
technique to measure magneto-transport properties of high-purity monolayer
WSe. We measure a record-high hole mobility of 80,000 cm/Vs and access
channel carrier densities as low as cm, an order of
magnitude lower than previously achievable. Our ability to realize transparent
contact to high-mobility devices at low density enables transport measurement
of correlation-driven quantum phases including observation of a low temperature
metal-insulator transition in a density and temperature regime where Wigner
crystal formation is expected, and observation of the fractional quantum Hall
effect under large magnetic fields. The charge transfer contact scheme paves
the way for discovery and manipulation of new quantum phenomena in 2D
semiconductors and their heterostructures
Direct visualization of the charge transfer in Graphene/-RuCl heterostructure
We investigate the electronic properties of a graphene and -ruthenium
trichloride (hereafter RuCl) heterostructure, using a combination of
experimental and theoretical techniques. RuCl is a Mott insulator and a
Kitaev material, and its combination with graphene has gained increasing
attention due to its potential applicability in novel electronic and
optoelectronic devices. By using a combination of spatially resolved
photoemission spectroscopy, low energy electron microscopy, and density
functional theory (DFT) calculations we are able to provide a first direct
visualization of the massive charge transfer from graphene to RuCl, which
can modify the electronic properties of both materials, leading to novel
electronic phenomena at their interface. The electronic band structure is
compared to DFT calculations that confirm the occurrence of a Mott transition
for RuCl. Finally, a measurement of spatially resolved work function allows
for a direct estimate of the interface dipole between graphene and RuCl.
The strong coupling between graphene and RuCl could lead to new ways of
manipulating electronic properties of two-dimensional lateral heterojunction.
Understanding the electronic properties of this structure is pivotal for
designing next generation low-power opto-electronics devices
Nanometer-Scale Lateral pân Junctions in Graphene/α-RuCl3 Heterostructures
[EN] The ability to create nanometer-scale lateral p-n junctions is essential for the next generation of two-dimensional (2D) devices. Using the charge-transfer heterostructure graphene/alpha-RuCl3, we realize nanoscale lateral p-n junctions in the vicinity of graphene nanobubbles. Our multipronged experimental approach incorporates scanning tunneling microscopy (STM) and spectroscopy (STS) and scattering-type scanning near-field optical microscopy (s-SNOM) to simultaneously probe the electronic and optical responses of nanobubble p-n junctions. Our STM/STS results reveal that p-n junctions with a band offset of 0.6 eV can be achieved with widths of 3 nm, giving rise to electric fields of order 108 V/m. Concurrent s-SNOM measurements validate a point-scatterer formalism for modeling the interaction of surface plasmon polaritons (SPPs) with nanobubbles. Ab initio density functional theory (DFT) calculations corroborate our experimental data and reveal the dependence of charge transfer on layer separation. Our study provides experimental and conceptual foundations for generating p-n nanojunctions in 2D materials.Research at Columbia University was supported as part of the Energy Frontier Research Center on Programmable Quantum Materials funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under Award No DE-SC0019443. Plasmonic nano-imaging at Columbia University was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under Award No DE-SC0018426. J.Z. and A.R. were supported by the European Research Council (ERC-2015-AdG694097), the Cluster of Excellence âAdvanced Imaging of Matterâ (AIM) EXC 2056-390715994, funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under RTG 2247, Grupos Consolidados (IT1249-19), and SFB925 âLight induced dynamics and control of correlated quantum systemsâ. J.Z. and A.R. would like to acknowledge Nicolas Tancogne-Dejean and Lede Xian for fruitful discussions and also acknowledge support by the Max Planck Institute-New York City Center for Non-Equilibrium Quantum Phenomena. The Flatiron Institute is a division of the Simons Foundation. J.Z. acknowledges funding received from the European Union Horizon 2020 research and innovation programme under Marie SkĆodowska-Curie Grant Agreement 886291 (PeSD-NeSL). STM support was provided by the National Science Foundation via Grant DMR-2004691. C.R.-V. acknowledges funding from the European Union Horizon 2020 research and innovation programme under the Marie SkĆodowska-Curie Grant Agreement 844271. D.G.M. acknowledges support from the Gordon and Betty Moore Foundationâs EPiQS Initiative, Grant GBMF9069. J.Q.Y. was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. S.E.N. acknowledges support from the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Division of Scientific User Facilities. Work at University of Tennessee was supported by NSF Grant 180896
Nanometer-scale lateral p-n junctions in graphene/α-RuCl3 heterostructures
The ability to create nanometer-scale lateral pân junctions is essential for the next generation of two-dimensional (2D) devices. Using the charge-transfer heterostructure graphene/α-RuCl3, we realize nanoscale lateral pân junctions in the vicinity of graphene nanobubbles. Our multipronged experimental approach incorporates scanning tunneling microscopy (STM) and spectroscopy (STS) and scattering-type scanning near-field optical microscopy (s-SNOM) to simultaneously probe the electronic and optical responses of nanobubble pân junctions. Our STM/STS results reveal that pân junctions with a band offset of âŒ0.6 eV can be achieved with widths of âŒ3 nm, giving rise to electric fields of order 108 V/m. Concurrent s-SNOM measurements validate a point-scatterer formalism for modeling the interaction of surface plasmon polaritons (SPPs) with nanobubbles. Ab initio density functional theory (DFT) calculations corroborate our experimental data and reveal the dependence of charge transfer on layer separation. Our study provides experimental and conceptual foundations for generating pân nanojunctions in 2D materials.Research at Columbia University was supported as part of the Energy Frontier Research Center on Programmable Quantum Materials funded by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under Award No DE-SC0019443. Plasmonic nano-imaging at Columbia University was supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), under Award No DE-SC0018426. J.Z. and A.R. were supported by the European Research Council (ERC-2015-AdG694097), the Cluster of Excellence âAdvanced Imaging of Matterâ (AIM) EXC 2056-390715994, funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under RTG 2247, Grupos Consolidados (IT1249-19), and SFB925 âLight induced dynamics and control of correlated quantum systemsâ. J.Z. and A.R. would like to acknowledge Nicolas Tancogne-Dejean and Lede Xian for fruitful discussions and also acknowledge support by the Max Planck Institute-New York City Center for Non-Equilibrium Quantum Phenomena. The Flatiron Institute is a division of the Simons Foundation. J.Z. acknowledges funding received from the European Union Horizon 2020 research and innovation programme under Marie SkĆodowska-Curie Grant Agreement 886291 (PeSD-NeSL). STM support was provided by the National Science Foundation via Grant DMR-2004691. C.R.-V. acknowledges funding from the European Union Horizon 2020 research and innovation programme under the Marie SkĆodowska-Curie Grant Agreement 844271. D.G.M. acknowledges support from the Gordon and Betty Moore Foundationâs EPiQS Initiative, Grant GBMF9069. J.Q.Y. was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division. S.E.N. acknowledges support from the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Division of Scientific User Facilities. Work at University of Tennessee was supported by NSF Grant 180896.Peer reviewe
Ultra-sharp lateral p-n junctions in modulation-doped graphene
We demonstrate ultra-sharp (âČ10 nm) lateral p-n junctions in graphene using electronic transport, scanning tunneling microscopy, and first principles calculations. The p-n junction lies at the boundary between differentially-doped regions of a graphene sheet, where one side is intrinsic and the other is charge-doped by proximity to a flake of α-RuCl3 across a thin insulating barrier. We extract the p-n junction contribution to the device resistance to place bounds on the junction width. We achieve an ultra-sharp junction when the boundary between the intrinsic and doped regions is defined by a cleaved crystalline edge of α-RuCl3 located 2 nm from the graphene. Scanning tunneling spectroscopy in heterostructures of graphene, hexagonal boron nitride, and α-RuCl3 shows potential variations on a sub-10 nm length scale. First principles calculations reveal the charge-doping of graphene decays sharply over just nanometers from the edge of the α-RuCl3 flake
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Direct Visualization of the Charge Transfer in a Graphene/α-RuCl3 Heterostructure via Angle-Resolved Photoemission Spectroscopy.
We investigate the electronic properties of a graphene and α-ruthenium trichloride (α-RuCl3) heterostructure using a combination of experimental techniques. α-RuCl3 is a Mott insulator and a Kitaev material. Its combination with graphene has gained increasing attention due to its potential applicability in novel optoelectronic devices. By using a combination of spatially resolved photoemission spectroscopy and low-energy electron microscopy, we are able to provide a direct visualization of the massive charge transfer from graphene to α-RuCl3, which can modify the electronic properties of both materials, leading to novel electronic phenomena at their interface. A measurement of the spatially resolved work function allows for a direct estimate of the interface dipole between graphene and α-RuCl3. Their strong coupling could lead to new ways of manipulating electronic properties of a two-dimensional heterojunction. Understanding the electronic properties of this structure is pivotal for designing next generation low-power optoelectronics devices
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Polaritonic Probe of an Emergent 2D Dipole Interface
The use of work-function-mediated charge transfer has recently emerged as a reliable route toward nanoscale electrostatic control of individual atomic layers. Using α-RuCl3 as a 2D electron acceptor, we are able to induce emergent nano-optical behavior in hexagonal boron nitride (hBN) that arises due to interlayer charge polarization. Using scattering-type scanning near-field optical microscopy (s-SNOM), we find that a thin layer of α-RuCl3 adjacent to an hBN slab reduces the propagation length of hBN phonon polaritons (PhPs) in significant excess of what can be attributed to intrinsic optical losses. Concomitant nano-optical spectroscopy experiments reveal a novel resonance that aligns energetically with the region of excess PhP losses. These experimental observations are elucidated by first-principles density-functional theory and near-field model calculations, which show that the formation of a large interfacial dipole suppresses out-of-plane PhP propagation. Our results demonstrate the potential utility of charge-transfer heterostructures for tailoring optoelectronic properties of 2D insulators