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Controlling a Van Hove singularity and Fermi surface topology at a complex oxide heterostructure interface.
The emergence of saddle-point Van Hove singularities (VHSs) in the density of states, accompanied by a change in Fermi surface topology, Lifshitz transition, constitutes an ideal ground for the emergence of different electronic phenomena, such as superconductivity, pseudo-gap, magnetism, and density waves. However, in most materials the Fermi level, [Formula: see text], is too far from the VHS where the change of electronic topology takes place, making it difficult to reach with standard chemical doping or gating techniques. Here, we demonstrate that this scenario can be realized at the interface between a Mott insulator and a band insulator as a result of quantum confinement and correlation enhancement, and easily tuned by fine control of layer thickness and orbital occupancy. These results provide a tunable pathway for Fermi surface topology and VHS engineering of electronic phases
Orbital character effects in the photon energy and polarization dependence of pure C60 photoemission
Recent direct experimental observation of multiple highly-dispersive C
valence bands has allowed for a detailed analysis of the unique photoemission
traits of these features through photon energy- and polarization-dependent
measurements. Previously obscured dispersions and strong photoemission traits
are now revealed by specific light polarizations. The observed intensity
effects prove the locking in place of the C molecules at low
temperatures and the existence of an orientational order imposed by the
substrate chosen. Most importantly, photon energy- and polarization-dependent
effects are shown to be intimately linked with the orbital character of the
C band manifolds which allows for a more precise determination of the
orbital character within the HOMO-2. Our observations and analysis provide
important considerations for the connection between molecular and crystalline
C electronic structure, past and future band structure studies, and for
increasingly popular C electronic device applications, especially those
making use of heterostructures
Temperature-Dependent Electron-Electron Interaction in Graphene on SrTiO3
The electron band structure of graphene on SrTiO3 substrate has been
investigated as a function of temperature. The high-resolution angle-resolved
photoemission study reveals that the spectral width at Fermi energy and the
Fermi velocity of graphene on SrTiO3 are comparable to those of graphene on a
BN substrate. Near the charge neutrality, the energy-momentum dispersion of
graphene exhibits a strong deviation from the well-known linearity, which is
magnified as temperature decreases. Such modification resembles the
characteristics of enhanced electron-electron interaction. Our results not only
suggest that SrTiO3 can be a plausible candidate as a substrate material for
applications in graphene-based electronics, but also provide a possible route
towards the realization of a new type of strongly correlated electron phases in
the prototypical two-dimensional system via the manipulation of temperature and
a proper choice of dielectric substrates.Comment: 16 pages, 3 figure
Evidence for quasi-one-dimensional charge density wave in CuTe by angle-resolved photoemission spectroscopy
We report the electronic structure of CuTe with a high charge density wave
(CDW) transition temperature Tc = 335 K by angle-resolved photoemission
spectroscopy (ARPES). An anisotropic charge density wave gap with a maximum
value of 190 meV is observed in the quasi-one-dimensional band formed by Te px
orbitals. The CDW gap can be filled by increasing temperature or electron
doping through in situ potassium deposition. Combining the experimental results
with calculated electron scattering susceptibility and phonon dispersion, we
suggest that both Fermi surface nesting and electron-phonon coupling play
important roles in the emergence of the CDW
Observation of a flat and extended surface state in a topological semimetal
A topological flatband, also known as drumhead states, is an ideal platform
to drive new exotic topological quantum phases. Using angle-resolved
photoemission spectroscopy experiments, we reveal the emergence of a highly
localized possible drumhead surface state in a topological semimetal BaAl4 and
provide its full energy and momentum space topology. We find that the observed
surface state is highly localized in momentum, inside a square-shaped bulk
Dirac nodal loop, and in energy, leading to a flat band and a peak in the
density of state. These results establish this class of materials as a possible
experimental realization of drumhead surface states and provide an important
reference for future studies of fundamental physics of topological quantum
phase transition
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