18 research outputs found
Fuzzy Jets
Collimated streams of particles produced in high energy physics experiments
are organized using clustering algorithms to form jets. To construct jets, the
experimental collaborations based at the Large Hadron Collider (LHC) primarily
use agglomerative hierarchical clustering schemes known as sequential
recombination. We propose a new class of algorithms for clustering jets that
use infrared and collinear safe mixture models. These new algorithms, known as
fuzzy jets, are clustered using maximum likelihood techniques and can
dynamically determine various properties of jets like their size. We show that
the fuzzy jet size adds additional information to conventional jet tagging
variables. Furthermore, we study the impact of pileup and show that with some
slight modifications to the algorithm, fuzzy jets can be stable up to high
pileup interaction multiplicities
Evidence for topological surface states in amorphous BiSe
Crystalline symmetries have played a central role in the identification of
topological materials. The use of symmetry indicators and band representations
have enabled a classification scheme for crystalline topological materials,
leading to large scale topological materials discovery. In this work we address
whether amorphous topological materials, which lie beyond this classification
due to the lack of long-range structural order, exist in the solid state. We
study amorphous BiSe thin films, which show a metallic behavior and
an increased bulk resistance. The observed low field magnetoresistance due to
weak antilocalization demonstrates a significant number of two dimensional
surface conduction channels. Our angle-resolved photoemission spectroscopy data
is consistent with a dispersive two-dimensional surface state that crosses the
bulk gap. Spin resolved photoemission spectroscopy shows this state has an
anti-symmetric spin-texture resembling that of the surface state of crystalline
BiSe. These experimental results are consistent with theoretical
photoemission spectra obtained with an amorphous tight-binding model that
utilizes a realistic amorphous structure. This discovery of amorphous materials
with topological properties uncovers an overlooked subset of topological matter
outside the current classification scheme, enabling a new route to discover
materials that can enhance the development of scalable topological devices.Comment: 40 pages (21 main + 19 supplemental), 15 figures (4 main + 11
supplemental
Correlation-Driven Electron-Hole Asymmetry in Graphene Field Effect Devices
Electron-hole asymmetry is a fundamental property in solids that can
determine the nature of quantum phase transitions and the regime of operation
for devices. The observation of electron-hole asymmetry in graphene and
recently in the phase diagram of bilayer graphene has spurred interest into
whether it stems from disorder or from fundamental interactions such as
correlations. Here, we report an effective new way to access electron-hole
asymmetry in 2D materials by directly measuring the quasiparticle self-energy
in graphene/Boron Nitride field effect devices. As the chemical potential moves
from the hole to the electron doped side, we see an increased strength of
electronic correlations manifested by an increase in the band velocity and
inverse quasiparticle lifetime. These results suggest that electronic
correlations play an intrinsic role in driving electron hole asymmetry in
graphene and provide a new insight for asymmetries in more strongly correlated
materials.Comment: 22 pages, 7 figure
Polarization dependent photoemission as a probe of the magnetic ground state in the layered ferromagnet VI3
Layered ferromagnets are thrilling materials from both a fundamental and
technological point of view. VI3 is an interesting example, with a complex
magnetism that differentiates it from the first reported Cr based layered
ferromagnets. Here, we show in an indirect way through Angle Resolved
Photoemission Spectroscopy (ARPES) experiments, the importance of spin-orbit
coupling setting the electronic properties of this material. Our light
polarized photoemission measurements point to a ground state with a half-filled
e'_+- doublet, where a gap opening is triggered by spin-orbit coupling enhanced
by electronic correlations
Visualizing electron localization of WS2/WSe2 moiré superlattices in momentum space.
The search for materials with flat electronic bands continues due to their potential to drive strong correlation and symmetry breaking orders. Electronic moirés formed in van der Waals heterostructures have proved to be an ideal platform. However, there is no holistic experimental picture for how superlattices modify electronic structure. By combining spatially resolved angle-resolved photoemission spectroscopy with optical spectroscopy, we report the first direct evidence of how strongly correlated phases evolve from a weakly interacting regime in a transition metal dichalcogenide superlattice. By comparing short and long wave vector moirés, we find that the electronic structure evolves into a highly localized regime with increasingly flat bands and renormalized effective mass. The flattening is accompanied by the opening of a large gap in the spectral function and splitting of the exciton peaks. These results advance our understanding of emerging phases in moiré superlattices and point to the importance of interlayer physics