5,741 research outputs found
Effect of impurity substitution on band structure and mass renormalization of the correlated FeTeSe superconductor
Using angle-resolved photoemission spectroscopy (ARPES), we studied the
effect of the impurity potential on the electronic structure of
FeTeSe superconductor by substituting 10\% of Ni for Fe which
leads to an electron doping of the system. We could resolve three hole pockets
near the zone center and an electron pocket near the zone corner in the case of
FeTeSe, whereas only two hole pockets near the zone center and
an electron pocket near the zone corner are resolved in the case of
FeNiTeSe, suggesting that the hole pocket
having predominantly the orbital character is very sensitive to the
impurity scattering. Upon electron doping, the size of the hole pockets
decrease and the size of the electron pockets increase as compared to the host
compound. However, the observed changes in the size of the electron and hole
pockets are not consistent with the rigid-band model. Moreover, the effective
mass of the hole pockets is reduced near the zone center and of the electron
pockets is increased near the zone corner in the doped
FeNiTeSe as compared to FeTeSe.
We refer these observations to the changes of the spectral function due to the
effect of the impurity potential of the dopants.Comment: 8 pages, 3 figure
Origin of the peak-dip-hump structure in the photoemission spectra of Bi2212
The famous peak-dip-hump lineshape of the (\pi,0) photoemission spectrum of
the bilayer Bi HTSC in the superconducting state is shown to be a superposition
of spectral features originating from different electronic states which reside
at different binding energies, but are each describable by essentially
identical single-particle spectral functions. The 'superconducting' peak is due
to the antibonding Cu-O-related band, while the hump is mainly formed by its
bonding counterpart, with a c-axis bilayer coupling induced splitting of about
140 meV.Comment: 5 pages: text + 4 figures, revtex (Fig.2 is replaced by more suitable
one
Unadulterated spectral function of low energy quasiparticles: Bi-2212, nodal direction
Fitting the momentum distribution photoemission spectra to the Voigt profile
appears to be a robust procedure to purify the interaction effects from the
experimental resolution. In application to Bi-2212 high-Tc cuprates, the
procedure reveals the true scattering rate at low binding energies and
temperatures, and, consequently, the true value of the elastic scattering.
Reaching the minimal value ~ 16 meV, the elastic scattering does not reveal a
systematic dependence on doping level, but is rather sensitive to impurity
concentration, and can be explained by the forward scattering on out-of-plane
impurities. The inelastic scattering is found to form well-defined
quasiparticles with the quadratic and cubic energy dependence of the scattering
rate above and below Tc, respectively. The observed energy-temperature
asymmetry of the scattering rate is also discussed.Comment: 4 revtex pages, 4 figure
Quantitative spectral analysis of the sdB star HD 188112: a helium-core white dwarf progenitor
HD 188112 is a bright (V = 10.2 mag) hot subdwarf B (sdB) star with a mass
too low to ignite core helium burning and is therefore considered as a
pre-extremely low mass (ELM) white dwarf (WD). ELM WDs (M 0.3 Msun) are
He-core objects produced by the evolution of compact binary systems. We present
in this paper a detailed abundance analysis of HD 188112 based on
high-resolution Hubble Space Telescope (HST) near and far-ultraviolet
spectroscopy. We also constrain the mass of the star's companion. We use hybrid
non-LTE model atmospheres to fit the observed spectral lines and derive the
abundances of more than a dozen elements as well as the rotational broadening
of metallic lines. We confirm the previous binary system parameters by
combining radial velocities measured in our UV spectra with the already
published ones. The system has a period of 0.60658584 days and a WD companion
with M 0.70 Msun. By assuming a tidally locked rotation, combined with
the projected rotational velocity (v sin i = 7.9 0.3 km s) we
constrain the companion mass to be between 0.9 and 1.3 Msun. We further discuss
the future evolution of the system as a potential progenitor of a
(underluminous) type Ia supernova. We measure abundances for Mg, Al, Si, P, S,
Ca, Ti, Cr, Mn, Fe, Ni, and Zn, as well as for the trans-iron elements Ga, Sn,
and Pb. In addition, we derive upper limits for the C, N, O elements and find
HD 188112 to be strongly depleted in carbon. We find evidence of non-LTE
effects on the line strength of some ionic species such as Si II and Ni II. The
metallic abundances indicate that the star is metal-poor, with an abundance
pattern most likely produced by diffusion effects.Comment: Accepted for publication in A&
Constituents of the "kink" in high-Tc cuprates
Applying the Kramers-Kronig consistent procedure, developed earlier, we
investigate in details the formation of the quasiparticle spectrum along the
nodal direction of high-Tc cuprates. The heavily discussed "70 meV kink" on the
renormalized dispersion exhibits a strong temperature and doping dependence
when purified from structural effects. This dependence is well understood in
terms of fermionic and bosonic constituents of the self-energy. The latter
follows the evolution of the spin-fluctuation spectrum, emerging below T* and
sharpening below Tc, and is the main responsible for the formation of the kink
in question.Comment: revte
Optical tomography of Fock state superpositions
We consider optical tomography of photon Fock state superpositions in
connection with recent experimental achievements. The emphasis is put on the
fact that it suffices to represent the measured tomogram as a main result of
the experiment. We suggest a test for checking the correctness of experimental
data. Explicit expressions for optical tomograms of Fock state superpositions
are given in terms of Hermite polynomials. Particular cases of vacuum and low
photon-number state superposition are considered as well as influence of
thermal noise on state purity is studied.Comment: 5 pages, 2 figure
Disentangling surface and bulk photoemission using circularly polarized light
We show that in the angle resolved photoemission spectroscopy (ARPES)
near-surface induced fields can be useful for disentangling the surface and
bulk related emission. The jump of the dielectric function at the interface
results in a nonzero term in the photoemission
matrix element. The term happens to be significant approximately within the
first unit cell and leads to the circular dichroism for the states localized
therein. As an example we use ARPES spectra of an YBaCuO
crystal to distinguish between the overdoped surface related component and its
bulk counterparts.Comment: 4 pages, 2 figure
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