846 research outputs found
Note on finite temperature sum rules for vector and axial-vector spectral functions
An updated analysis of vector and axial-vector spectral functions is
presented. The resonant contributions to the spectral integrals are shown to be
expressible as multiples of 4 pi^2 f_pi^2, encoding the scale of spontaneous
chiral symmetry breaking in QCD. Up to order T^2 this behavior carries over to
the case of finite temperature.Comment: 10 pages, 2 figure
Extracting the Temperature of Hot Carriers in Time- and Angle-Resolved Photoemission
The interaction of light with a material's electronic system creates an
out-of-equilibrium (non-thermal) distribution of optically excited electrons.
Non-equilibrium dynamics relaxes this distribution on an ultrafast timescale to
a hot Fermi-Dirac distribution with a well-defined temperature. The advent of
time- and angle-resolved photoemission spectroscopy (TR-ARPES) experiments has
made it possible to track the decay of the temperature of the excited hot
electrons in selected states in the Brillouin zone, and to reveal their cooling
in unprecedented detail in a variety of emerging materials. It is, however, not
a straightforward task to determine the temperature with high accuracy. This is
mainly attributable to an a priori unknown position of the Fermi level and the
fact that the shape of the Fermi edge can be severely perturbed when the state
in question is crossing the Fermi energy. Here, we introduce a method that
circumvents these difficulties and accurately extracts both the temperature and
the position of the Fermi level for a hot carrier distribution by tracking the
occupation statistics of the carriers measured in a TR-ARPES experiment.Comment: 17 pages, 5 figure
Simultaneous quantization of bulk conduction and valence states through adsorption of nonmagnetic impurities on Bi2Se3
Exposing the (111) surface of the topological insulator Bi2Se3 to carbon
monoxide results in strong shifts of the features observed in angle-resolved
photoemission. The behavior is very similar to an often reported `aging' effect
of the surface and it is concluded that this aging is most likely due to the
adsorption of rest gas molecules. The spectral changes are also similar to
those recently reported in connection with the adsorption of the magnetic
adatom Fe. All spectral changes can be explained by a simultaneous confinement
of the conduction band and valence band states. This is only possible because
of the unusual bulk electronic structure of Bi2Se3. The valence band
quantization leads to spectral features which resemble those of a band gap
opening at the Dirac point.Comment: 5 pages, 4 figure
Surface states on a topologically non-trivial semimetal: The case of Sb(110)
The electronic structure of Sb(110) is studied by angle-resolved
photoemission spectroscopy and first-principle calculations, revealing several
electronic surface states in the projected bulk band gaps around the Fermi
energy. The dispersion of the states can be interpreted in terms of a strong
spin-orbit splitting. The bulk band structure of Sb has the characteristics of
a strong topological insulator with a Z2 invariant nu0=1. This puts constraints
on the existence of metallic surface states and the expected topology of the
surface Fermi contour. However, bulk Sb is a semimetal, not an insulator and
these constraints are therefore partly relaxed. This relation of bulk topology
and expected surface state dispersion for semimetals is discussed.Comment: 7 pages, 4 figure
Pseudodoping of Metallic Two-Dimensional Materials by The Supporting Substrates
We demonstrate how hybridization between a two-dimensional material and its
substrate can lead to an apparent heavy doping, using the example of monolayer
TaS grown on Au(111). Combining calculations, scanning
tunneling spectroscopy experiments and a generic model, we show that strong
changes in Fermi areas can arise with much smaller actual charge transfer. This
mechanism, which we refer to as pseudodoping, is a generic effect for metallic
two-dimensional materials which are either adsorbed to metallic substrates or
embedded in vertical heterostructures. It explains the apparent heavy doping of
TaS on Au(111) observed in photoemission spectroscopy and spectroscopic
signatures in scanning tunneling spectroscopy. Pseudodoping is associated with
non-linear energy-dependent shifts of electronic spectra, which our scanning
tunneling spectroscopy experiments reveal for clean and defective TaS
monolayer on Au(111). The influence of pseudodoping on the formation of charge
ordered, magnetic, or superconducting states is analyzed.Comment: arXiv admin note: substantial text overlap with arXiv:1609.0022
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