17 research outputs found
Cu doping effects on the electronic structure of Fe1-xCuxSe
Using angle-resolved photoemission spectroscopy (ARPES), we studied the
evolution of the electronic structure of Fe1-xCuxSe from x = 0 to 0.10. We
found that the Cu dopant introduces extra electron carriers. The hole bands
near the gamma point are observed to steadily shift downward with increasing
doping and completely sink down below the Fermi level (EF) for x > 0.05.
Meanwhile, the electron pocket near the M point becomes larger but loses the
spectral weight near EF. We also observed that effective mass of the electron
band near the M point increases with doping. Our result explains why
superconductivity disappears and metal insulator transition (MIT) like behavior
occurs upon Cu doping in terms of electronic structure, and provide insight
into emergent magnetic fluctuation in Fe1-xCuxSe
Effect of the sample work function on alkali metal dosing induced electronic structure change
Alkali metal dosing (AMD) has been widely used as a way to control doping
without chemical substitution. This technique, in combination with angle
resolved photoemission spectroscopy (ARPES), often provides an opportunity to
observe unexpected phenomena. However, the amount of transferred charge and the
corresponding change in the electronic structure vary significantly depending
on the material. Here, we report study on the correlation between the sample
work function and alkali metal induced electronic structure change for three
iron-based superconductors: FeSe, Ba(FeCo)As and
NaFeAs which share a similar Fermi surface topology. Electronic structure
change upon monolayer of alkali metal dosing and the sample work function were
measured by ARPES. Our results show that the degree of electronic structure
change is proportional to the difference between the work function of the
sample and Mulliken's absolute electronegativity of the dosed alkali metal.
This finding provides a possible way to estimate the AMD induced electronic
structure change.Comment: 4 page
Deep learning-based statistical noise reduction for multidimensional spectral data
In spectroscopic experiments, data acquisition in multi-dimensional phase
space may require long acquisition time, owing to the large phase space volume
to be covered. In such case, the limited time available for data acquisition
can be a serious constraint for experiments in which multidimensional spectral
data are acquired. Here, taking angle-resolved photoemission spectroscopy
(ARPES) as an example, we demonstrate a denoising method that utilizes deep
learning as an intelligent way to overcome the constraint. With readily
available ARPES data and random generation of training data set, we
successfully trained the denoising neural network without overfitting. The
denoising neural network can remove the noise in the data while preserving its
intrinsic information. We show that the denoising neural network allows us to
perform similar level of second-derivative and line shape analysis on data
taken with two orders of magnitude less acquisition time. The importance of our
method lies in its applicability to any multidimensional spectral data that are
susceptible to statistical noise.Comment: 8 pages, 8 figure
Quantum electron liquid and its possible phase transition
Purely quantum electron systems exhibit intriguing correlated electronic
phases by virtue of quantum fluctuations in addition to electron-electron
interactions. To realize such quantum electron systems, a key ingredient is
dense electrons decoupled from other degrees of freedom. Here, we report the
discovery of a pure quantum electron liquid, which spreads up to ~ 3 {\AA} in
the vacuum on the surface of electride crystal. An extremely high electron
density and its weak hybridisation with buried atomic orbitals evidence the
quantum and pure nature of electrons, that exhibit a polarized liquid phase as
demonstrated by our spin-dependent measurement. Further, upon enhancing the
electron correlation strength, the dynamics of quantum electrons changes to
that of non-Fermi liquid along with an anomalous band deformation, suggestive
of a transition to a hexatic liquid crystal phase. Our findings cultivate the
frontier of quantum electron systems, and serve as a platform for exploring
correlated electronic phases in a pure fashion.Comment: 29 pages, 4 figures, 10 extended data figure
Sign-tunable anomalous Hall effect induced by two-dimensional symmetry-protected nodal structures in ferromagnetic perovskite oxide thin films
Magnetism and spin-orbit coupling (SOC) are two quintessential ingredients
underlying novel topological transport phenomena in itinerant ferromagnets.
When spin-polarized bands support nodal points/lines with band degeneracy that
can be lifted by SOC, the nodal structures become a source of Berry curvature;
this leads to a large anomalous Hall effect (AHE). Contrary to
three-dimensional systems that naturally host nodal points/lines,
two-dimensional (2D) systems can possess stable nodal structures only when
proper crystalline symmetry exists. Here we show that 2D spin-polarized band
structures of perovskite oxides generally support symmetry-protected nodal
lines and points that govern both the sign and the magnitude of the AHE. To
demonstrate this, we performed angle-resolved photoemission studies of
ultrathin films of SrRuO, a representative metallic ferromagnet with SOC.
We show that the sign-changing AHE upon variation in the film thickness,
magnetization, and chemical potential can be well explained by theoretical
models. Our study is the first to directly characterize the topological band
structure of 2D spin-polarized bands and the corresponding AHE, which could
facilitate new switchable devices based on ferromagnetic ultrathin films
Electronic band structure of (111) thin filman angle-resolved photoemission spectroscopy study
We studied the electronic band structure of pulsed laser deposition (PLD)
grown (111)-oriented SrRuO (SRO) thin films using \textit{in situ}
angle-resolved photoemission spectroscopy (ARPES) technique. We observed
previously unreported, light bands with a renormalized quasiparticle effective
mass of about 0.8. The electron-phonon coupling underlying this mass
renormalization yields a characteristic "kink" in the band dispersion. The
self-energy analysis using the Einstein model suggests five optical phonon
modes covering an energy range 44 to 90 meV contribute to the coupling.
Besides, we show that the quasiparticle spectral intensity at the Fermi level
is considerably suppressed, and two prominent peaks appear in the valance band
spectrum at binding energies of 0.8 eV and 1.4 eV, respectively. We discuss the
possible implications of these observations. Overall, our work demonstrates
that high-quality thin films of oxides with large spin-orbit coupling can be
grown along the polar (111) orientation by the PLD technique, enabling
\textit{in situ} electronic band structure study. This could allow for
characterizing the thickness-dependent evolution of band structure of (111)
heterostructuresa prerequisite for exploring possible topological quantum
states in the bilayer limit
Magnetic field detwinning in feTe
© 2019, Korea Institute of Applied Superconductivity and Cryogenics. All rights reserved.Iron-based superconductors (IBSs) possess nematic phases in which rotational symmetry of the electronic structure is spontaneously broken. This novel phase has attracted much attention as it is believed to be closely linked to the superconductivity. However, observation of the symmetry broken phase by using a macroscopic experimental tool is a hard task because of naturally formed twin domains. Here, we report on a novel detwinning method by using a magnetic field on FeTe single crystal. Detwinning effect was measured by resistivity anisotropy using the Montgomery method. Our results show that FeTe was detwinned at 2T, which is a relatively weak field compared to the previously reported result. Furthermore, detwinning effect is retained even when the field is turned off after field cooling, making it an external stimulation-free detwinning metho
Cu doping effects on the electronic structure of Fe1-x CuxSe
Using angle-resolved photoemission spectroscopy, we investigated the evolution of the electronic structure of Fe1-xCuxSe from x=0 to 0.10. We found that the substitution of Fe by Cu introduces extra electron carriers. The hole bands near the Γ point were observed to shift downward with increasing doping x and completely sank down below the Fermi level (EF) for x≥0.05. Meanwhile, the electron pockets near the M point became larger but lost the spectral weight near EF. Concomitantly, the effective mass of the electron bands increased with doping. Our results show how a metal-insulator transition behavior occurs upon Cu doping in view of the electronic structure and provide a platform to further investigation on the origin of emergent magnetic fluctuation in Fe1-xCuxSe.11Nsciescopu