923 research outputs found
Ultrafast photodoping and effective Fermi-Dirac distribution of the Dirac particles in Bi2Se3
We exploit time- and angle- resolved photoemission spectroscopy to determine
the evolution of the out-of-equilibrium electronic structure of the topological
insulator Bi2Se. The response of the Fermi-Dirac distribution to ultrashort IR
laser pulses has been studied by modelling the dynamics of the hot electrons
after optical excitation. We disentangle a large increase of the effective
temperature T* from a shift of the chemical potential mu*, which is consequence
of the ultrafast photodoping of the conduction band. The relaxation dynamics of
T* and mu* are k-independent and these two quantities uniquely define the
evolution of the excited charge population. We observe that the energy
dependence of the non-equilibrium charge population is solely determined by the
analytical form of the effective Fermi-Dirac distribution.Comment: 5 Pages, 3 Figure
Unusual Shubnikov-de Haas oscillations in BiTeCl
We report measurements of Shubnikov-de Haas (SdH) oscillations in single
crystals of BiTeCl at magnetic fields up to 31 T and at temperatures as low as
0.4 K. Two oscillation frequencies were resolved at the lowest temperatures,
Tesla and Tesla. We also measured the
infrared optical reflectance and Hall effect; we
propose that the two frequencies correspond respectively to the inner and outer
Fermi sheets of the Rashba spin-split bulk conduction band. The bulk carrier
concentration was cm and the effective
masses for the inner and for the
outer sheet. Surprisingly, despite its low effective mass, we found that the
amplitude of is very rapidly suppressed with increasing temperature,
being almost undetectable above K
Ultrafast Optical Control of the Electronic Properties of
We report on the temperature dependence of the electronic
properties, studied at equilibrium and out of equilibrium, by means of time and
angle resolved photoelectron spectroscopy. Our results unveil the dependence of
the electronic band structure across the Fermi energy on the sample
temperature. This finding is regarded as the dominant mechanism responsible for
the anomalous resistivity observed at T* 160 K along with the change of
the charge carrier character from holelike to electronlike. Having addressed
these long-lasting questions, we prove the possibility to control, at the
ultrashort time scale, both the binding energy and the quasiparticle lifetime
of the valence band. These experimental evidences pave the way for optically
controlling the thermoelectric and magnetoelectric transport properties of
BiTeCl and BiTeBr: a comparative high-pressure optical study
We here report a detailed high-pressure infrared transmission study of BiTeCl
and BiTeBr. We follow the evolution of two band transitions: the optical
excitation between two Rashba-split conduction bands, and the
absorption across the band gap. In the low pressure range, ~GPa,
for both compounds is approximately constant with pressure and
decreases, in agreement with band structure calculations. In BiTeCl, a clear
pressure-induced phase transition at 6~GPa leads to a different ground state.
For BiTeBr, the pressure evolution is more subtle, and we discuss the
possibility of closing and reopening of the band gap. Our data is consistent
with a Weyl phase in BiTeBr at 56~GPa, followed by the onset of a structural
phase transition at 7~GPa.Comment: are welcom
Evidence of reduced surface electron-phonon scattering in the conduction band of Bi_{2}Se_{3} by non-equilibrium ARPES
The nature of the Dirac quasiparticles in topological insulators calls for a
direct investigation of the electron-phonon scattering at the \emph{surface}.
By comparing time-resolved ARPES measurements of the TI Bi_{2}Se_{3} with
different probing depths we show that the relaxation dynamics of the electronic
temperature of the conduction band is much slower at the surface than in the
bulk. This observation suggests that surface phonons are less effective in
cooling the electron gas in the conduction band.Comment: 5 pages, 3 figure
The momentum and photon energy dependence of the circular dichroic photoemission in the bulk Rashba semiconductors BiTeX (X = I, Br, Cl)
Bulk Rashba systems BiTeX (X = I, Br, Cl) are emerging as important
candidates for developing spintronics devices, because of the coexistence of
spin-split bulk and surface states, along with the ambipolar character of the
surface charge carriers. The need of studying the spin texture of strongly
spin-orbit coupled materials has recently promoted circular dichroic Angular
Resolved Photoelectron Spectroscopy (cd-ARPES) as an indirect tool to measure
the spin and the angular degrees of freedom. Here we report a detailed photon
energy dependent study of the cd-ARPES spectra in BiTeX (X = I, Br and Cl). Our
work reveals a large variation of the magnitude and sign of the dichroism.
Interestingly, we find that the dichroic signal modulates differently for the
three compounds and for the different spin-split states. These findings show a
momentum and photon energy dependence for the cd-ARPES signals in the bulk
Rashba semiconductor BiTeX (X = I, Br, Cl). Finally, the outcome of our
experiment indicates the important relation between the modulation of the
dichroism and the phase differences between the wave-functions involved in the
photoemission process. This phase difference can be due to initial or final
state effects. In the former case the phase difference results in possible
interference effects among the photo-electrons emitted from different atomic
layers and characterized by entangled spin-orbital polarized bands. In the
latter case the phase difference results from the relative phases of the
expansion of the final state in different outgoing partial waves.Comment: 6 pages, 4 figure
Universal response of the type-II Weyl semimetals phase diagram
The discovery of Weyl semimetals represents a significant advance in
topological band theory. They paradigmatically enlarged the classification of
topological materials to gapless systems while simultaneously providing
experimental evidence for the long-sought Weyl fermions. Beyond fundamental
relevance, their high mobility, strong magnetoresistance, and the possible
existence of even more exotic effects, such as the chiral anomaly, make Weyl
semimetals a promising platform to develop radically new technology. Fully
exploiting their potential requires going beyond the mere identification of
materials and calls for a detailed characterization of their functional
response, which is severely complicated by the coexistence of surface- and
bulk-derived topologically protected quasiparticles, i.e., Fermi arcs and Weyl
points, respectively. Here, we focus on the type-II Weyl semimetal class where
we find a stoichiometry-dependent phase transition from a trivial to a
non-trivial regime. By exploring the two extreme cases of the phase diagram, we
demonstrate the existence of a universal response of both surface and bulk
states to perturbations. We show that quasi-particle interference patterns
originate from scattering events among surface arcs. Analysis reveals that
topologically non-trivial contributions are strongly suppressed by spin
texture. We also show that scattering at localized impurities generate
defect-induced quasiparticles sitting close to the Weyl point energy. These
give rise to strong peaks in the local density of states, which lift the Weyl
node significantly altering the pristine low-energy Weyl spectrum. Visualizing
the microscopic response to scattering has important consequences for
understanding the unusual transport properties of this class of materials.
Overall, our observations provide a unifying picture of the Weyl phase diagram
Momentum resolved spin dynamics of bulk and surface excited states in the topological insulator
The prospective of optically inducing a spin polarized current for spintronic
devices has generated a vast interest in the out-of-equilibrium electronic and
spin structure of topological insulators (TIs). In this Letter we prove that
only by measuring the spin intensity signal over several order of magnitude in
spin, time and angle resolved photoemission spectroscopy (STAR-PES) experiments
is it possible to comprehensively describe the optically excited electronic
states in TIs materials. The experiments performed on
reveal the existence of a Surface-Resonance-State in the 2nd bulk band gap
interpreted on the basis of fully relativistic ab-initio spin resolved
photoemission calculations. Remarkably, the spin dependent relaxation of the
hot carriers is well reproduced by a spin dynamics model considering two
non-interacting electronic systems, derived from the excited surface and bulk
states, with different electronic temperatures.Comment: 5 pages and 4 figure
Pharmacy practice research - A call to action.
Pharmacists have a societal duty of care. How to best provide that type of care requires scientific study. Pharmacy practice is a scientific discipline that studies the different aspects of the practice of pharmacy, and its impact on health care systems, medicine use, and patient care. Its scope has expanded globally to encompass clinical, behavioural, economic, and humanistic implications of the practice of pharmacy, as well as practice change and implementation in routine practice of innovations such as health interventions and patient-care services. The development, impact evaluation, implementation, and sustainability of health interventions and patient-care services represents a key research area for pharmacy practice. An approach for conducting these is provided. There is evidence that collaborative national and international research in this area is growing, showing an increased contribution to global health research. The role of universities and pharmacy professional associations in supporting the advancement of pharmacy through pharmacy practice research is also discussed. Finally, a call to action for pharmacy practice research, education, and practice is made
AntVideoRecord: Autonomous system to capture the locomotor activity of leafcutter ants
The leafcutter ants (LCA) are considered plague in a great part of the American continent,
causing great damage in production fields. Knowing the locomotion and foraging rhythm in
LCA on a continuous basis would imply a significant advance for ecological studies, fundamentally
of animal behavior. However, studying the forage rhythm of LCA in the field
involves a significant human effort. This also adds a risk of subjective results due to the
operator fatigue. In this work a new development named âAntVideoRecordâ is proposed
to address this issue. This device is a low-cost autonomous system that records videos of
the LCA path in a fixed position. The device can be easily reproduced using the freely accessible
source code provided. The evaluation of this novel device was successful because it
has exceeded all the basic requirements in the field: record continuously for at least seven
days, withstand high and low temperatures, capture acceptable videos during the day and
night, and have a simple configuration protocol by mobile devices and laptops. It was possible
to confirm the correct operation of the device, being able to record more than 1900 h
in the field at different climate conditions and times of the day.
2022 The Author(s). Published by Elsevier Ltd. This is an open access article under the CCANII: FMV 15605
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