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Tracking surface photovoltage dipole geometry in bi2se3 with time-resolved photoemission
Topological insulators have been shown to exhibit strong and long-lived surface photovoltages when excited by an infrared pump. The ability to generate long-lived potentials on these surfaces provides opportunities to manipulate the spin-momentum locked topological surface states. Moreover, the photo-induced nature of this effect allows for localized excitation of arbitrary geometries. Knowing precisely how these potentials form and evolve is critical in understanding how to manage the effect in applications. The uniqueness of the photoemission experimental geometry, in which the photoelectron must traverse the induced surface field in vacuum, provides an interesting probe of the electric dipole shape generated by the surface photovoltage. In this study, we are able to match the observed decay of the geometric effect on the photoelectron to an essential electrodynamics model of the light-induced dipole thereby tracking the fluence-dependent evolution of the dipole geometry. By utilizing a standard time-resolved angle-resolved photoemission experiment, we are able to determine real-space information of the dipole while simultaneously recovering time-resolved band structure
Magnetic ordering and fluctuation in kagome lattice antiferromagnets, Fe and Cr jarosites
Jarosite family compounds, KFe_3(OH)_6(SO_4)_2, (abbreviate Fe jarosite), and
KCr_3(OH)_6(SO_4)_2, (Cr jarosite), are typical examples of the Heisenberg
antiferromagnet on the kagome lattice and have been investigated by means of
magnetization and NMR experiments. The susceptibility of Cr jarosite deviates
from Curie-Weiss law due to the short-range spin correlation below about 150 K
and shows the magnetic transition at 4.2 K, while Fe jarosite has the
transition at 65 K. The susceptibility data fit well with the calculated one on
the high temperature expansion for the Heisenberg antiferromagnet on the kagome
lattice. The values of exchange interaction of Cr jarosite and Fe jarosite are
derived to be J_Cr = 4.9 K and J_Fe = 23 K, respectively. The 1H-NMR spectra of
Fe jarosite suggest that the ordered spin structure is the q = 0 type with
positive chirality of the 120 degrees configuration. The transition is caused
by a weak single-ion type anisotropy. The spin-lattice relaxation rate, 1/T_1,
of Fe jarosite in the ordered phase decreases sharply with lowering the
temperature and can be well explained by the two-magnon process of spin wave
with the anisotropy.Comment: REVTeX, 14 pages with 5 figures. Submitted to Canadian Journal of
Physic
Dendroclimatic Studies of White Spruce in the Yukon Territory, Canada
An extensive network of 111 white spruce tree-ring chronologies (2983 trees) from treeline sites was developed across the Yukon Territory and adjacent areas of Alaska and British Columbia. Ring-width series from 73 chronologies with adequate signal strength back to 1800 were analysed using correlation and Principal Component analyses. Although 50 chronologies showed a strong common growth pattern over the 1900-1950 period (45.6% of the variance in PC1), PC1 over the 1950-2000 period included only 22 (27.1% of the variance). Correlation with temperature data from the central-north Yukon indicated that 1900-1950 PC1 chronologies showed significant positive relationships to summer (JJA) minimum temperatures and strong negative relationships with prior summer maximum temperatures. Only four of these chronologies retained the positive summer signal for the 1950-2000 period and approximately one third exhibited significant negative responses to spring/summer minimum temperatures during the 1950-2000 period. The loss of positive temperature sensitivity indicates a divergent temperature response in ring width for most sites throughout the north and central Yukon, inhibiting the proposed temperature reconstruction from these data.
Analyses of 12 maximum latewood density (MXD) chronologies indicated that nine chronologies have significant relationships with summer maximum or mean temperatures prior to 1950 and six sites, in the central and southern Yukon, retained a slightly weaker but positive summer signal post-1950. Calibration against a regional temperature record (1938-2002) from the southern Yukon indicates that a regional MXD chronology from these six sites captures ca. 39% of the variance of summer (May-August) maximum temperatures. The first, MXD-based, summer maximum temperature reconstruction (1623-2002) was developed for the Yukon Territory. Most of the reconstruction is characterized by high frequency fluctuations with warmer and cooler intervals lasting rarely more than a decade, although the early portion (1630s-1750s) shows a more extended cooler period. This reconstruction showed similarities with the adjacent St. Elias-Wrangell Mountain reconstruction of July-September mean temperatures from Alaska particularly during the 17th and 19th centuries. These results indicate that MXD data are less influenced by divergence and could form the basis for a long temperature reconstruction in the Yukon
Dynamical scaling analysis of the optical Hall conductivity in the quantum Hall regime
Dynamical scaling analysis is theoretically performed for the ac (optical)
Hall conductivity as a function of Fermi
energy and frequency for the two-dimensional electron
gas and for graphene. In both systems, results based on exact diagonalization
show that displays a well-defined dynamical
scaling, for which the dynamical critical exponent as well as the localization
exponent are fitted and plugged in. A crossover from the dc-like bahavior to
the ac regime is identified. The dynamical scaling analysis has enabled us to
quantify the plateau in the ac Hall conductivity previously obtained, and to
predict that the plateaux structure in ac is robust enough to be observed in
the THz regime.Comment: 5 pages, 3 figure
Differential effects of male nutrient balance on pre- and post-copulatory traits, and consequences for female reproduction in Drosophila melanogaster
We thank Fleur Ponton and Stephen J. Simpson for the help during the early stages of the experiment, and Eleanor Bath and Irem Sepil for the help during the experiment. JM is funded by a DPhil scholarship from the Brazilian National Council for Scientific and Technological Development (CNPq) and SW is funded by NERC (NE/J018937/1) and BBSRC (BB/K014544/1) fellowships.Peer reviewedPublisher PD
The Boltzmann equation without angular cutoff in the whole space: II, Global existence for hard potential
As a continuation of our series works on the Boltzmann equation without
angular cutoff assumption, in this part, the global existence of solution to
the Cauchy problem in the whole space is proved in some suitable weighted
Sobolev spaces for hard potential when the solution is a small perturbation of
a global equilibrium
Regularizing effect and local existence for non-cutoff Boltzmann equation
The Boltzmann equation without Grad's angular cutoff assumption is believed
to have regularizing effect on the solution because of the non-integrable
angular singularity of the cross-section. However, even though so far this has
been justified satisfactorily for the spatially homogeneous Boltzmann equation,
it is still basically unsolved for the spatially inhomogeneous Boltzmann
equation. In this paper, by sharpening the coercivity and upper bound estimates
for the collision operator, establishing the hypo-ellipticity of the Boltzmann
operator based on a generalized version of the uncertainty principle, and
analyzing the commutators between the collision operator and some weighted
pseudo differential operators, we prove the regularizing effect in all (time,
space and velocity) variables on solutions when some mild regularity is imposed
on these solutions. For completeness, we also show that when the initial data
has this mild regularity and Maxwellian type decay in velocity variable, there
exists a unique local solution with the same regularity, so that this solution
enjoys the regularity for positive time
Global existence and full regularity of the Boltzmann equation without angular cutoff
We prove the global existence and uniqueness of classical solutions around an
equilibrium to the Boltzmann equation without angular cutoff in some Sobolev
spaces. In addition, the solutions thus obtained are shown to be non-negative
and in all variables for any positive time. In this paper, we study
the Maxwellian molecule type collision operator with mild singularity. One of
the key observations is the introduction of a new important norm related to the
singular behavior of the cross section in the collision operator. This norm
captures the essential properties of the singularity and yields precisely the
dissipation of the linearized collision operator through the celebrated
H-theorem
Tuning the electrically evaluated electron Lande g factor in GaAs quantum dots and quantum wells of different well widths
We evaluate the Lande g factor of electrons in quantum dots (QDs) fabricated
from GaAs quantum well (QW) structures of different well width. We first
determine the Lande electron g factor of the QWs through resistive detection of
electron spin resonance and compare it to the enhanced electron g factor
determined from analysis of the magneto-transport. Next, we form laterally
defined quantum dots using these quantum wells and extract the electron g
factor from analysis of the cotunneling and Kondo effect within the quantum
dots. We conclude that the Lande electron g factor of the quantum dot is
primarily governed by the electron g factor of the quantum well suggesting that
well width is an ideal design parameter for g-factor engineering QDs
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