4,702 research outputs found

### Electron Monte Carlo Simulations of Nanoporous Si Thin Films -- The Influence of Pore-Edge Charges

Electron transport within nanostructures can be important to varied
engineering applications, such as thermoelectrics and nanoelectronics. In
theoretical studies, electron Monte Carlo simulations are widely used as an
alternative approach to solving the electron Boltzmann transport equation,
where the energy-dependent electron scattering, exact structure shape, and
detailed electric field distribution can be fully incorporated. In this work,
such electron Monte Carlo simulations are employed to predict the electrical
conductivity of periodic nanoporous Si films that have been widely studied for
thermoelectric applications. The focus is on the influence of pore-edge charges
on the electron transport. The results are further compared to our previous
modeling [Hao et al., J. Appl. Phys. 121, 094308 (2017)], where the pore-edge
electric field has its own scattering rate to be added to the scattering rates
of other mechanisms

### Topological superconducting states in monolayer FeSe/SrTiO$_{3}$

The monolayer FeSe with a thickness of one unit cell grown on a
single-crystal SrTiO$_{3}$ substrate (FeSe/STO) exhibits striking
high-temperature superconductivity with transition temperature $T_{c}$ over 65K
reported by recent experimental measurements. In this work, through analyzing
the distinctive electronic structure, and providing systematic classification
of the pairing symmetry , we find that both $s$-and $p$-wave pairing with odd
parity give rise to topological superconducting states in monolayer FeSe, and
the exotic properties of $s$-wave topological superconducting states have close
relations with the unique non-symmorphic lattice structure which induces the
orbital-momentum locking. Our results indicate that the monolayer FeSe could be
in the topological nontrivial $s$-wave superconducting states if the relevant
effective pairing interactions are dominant in comparison with other
candidates.Comment: 11 pages, 4 figure

### Topological crystalline antiferromagnetic state in tetragonal FeS

Integration between magnetism and topology is an exotic phenomenon in
condensed-matter physics. Here, we propose an exotic phase named topological
crystalline antiferromagnetic state, in which antiferromagnetism intrinsically
integrates with nontrivial topology, and we suggest such a state can be
realized in tetragonal FeS. A combination of first-principles calculations and
symmetry analyses shows that the topological crystalline antiferromagnetic
state arises from band reconstruction induced by pair checker-board
antiferromagnetic order together with band-gap opening induced by intrinsic
spin-orbit coupling in tetragonal FeS. The topological crystalline
antiferromagnetic state is protected by the product of fractional translation
symmetry, mirror symmetry, and time-reversal symmetry, and present some unique
features. In contrast to strong topological insulators, the topological
robustness is surface-dependent. These findings indicate that non-trivial
topological states could emerge in pure antiferromagnetic materials, which
sheds new light on potential applications of topological properties in
fast-developing antiferromagnetic spintronics.Comment: 8 pages, 6 figure

### The Top Quark Production Asymmetries $A_{FB}^t$ and $A_{FB}^{\ell}$

A large forward-backward asymmetry is seen in both the top quark rapidity
distribution $A_{FB}^t$ and in the rapidity distribution of charged leptons
$A_{FB}^\ell$ from top quarks produced at the Tevatron. We study the kinematic
and dynamic aspects of the relationship of the two observables arising from the
spin correlation between the charged lepton and the top quark with different
polarization states. We emphasize the value of both measurements, and we
conclude that a new physics model which produces more right-handed than
left-handed top quarks is favored by the present data.Comment: accepted for publication in Physical Review Letter

### A General Analysis of Wtb anomalous Couplings

We investigate new physics effects on the Wtb effective couplings in a
model-independent manner. The new physics effects are summarized as four
independent couplings $f_1^L$, $f_1^R$, $f_2^L$ and $f_2^R$. Using
single-top-quark productions and W-helicity fraction measurements at the LHC
and Tevatron, we perform a global fit to impose constraints on top quark
effective couplings. We introduce a set of parameters $x_0$, $x_m$, $x_p$ and
$x_5$ to study the correlations among Wtb effective couplings. We show that (i)
improving the measurements of $\sigma_t$ and $\sigma_{tW}$ is important in
constraining the correlation of $(f_1^R,f_2^R)$ and $(f_2^L,f_2^R)$; (ii)
$f_1^L$ and $f_2^R$ are anti-correlated, which is sensitive to all the
experiments; (iii) $f_1^R$ and $f_2^L$ are also anti-correlated, which is
sensitive to the W-helicity measurements; (iv) the correlation between $f_2^L$
and $f_2^R$ is sensitive to the precision of $\sigma_t$, $\sigma_{tW}$ and
$F_0$ measurements. The effective Wtb couplings are studied in three kinds of
new physics models: $SU(2)_1 \times SU(2)_2 \times U(1)_X$ models, vector-like
quark models and Littlest Higgs model with and without T-parity. The Wtb
couplings in the left-right model and the un-unified model are sensitive to the
ratio of gauge couplings when the new heavy gauge boson's mass ($M_{W'}$) is
less than several hundred GeV, but the constraint is loose if $M_{W'}>1$ TeV.
The Wtb couplings in vector-like quark models and the Littlest Higgs models are
sensitive to the mixing angles of new heavy particles and SM particles. We also
include the constraints of the oblique T-parameter and Zbb couplings which
impose much tighter constraints on the mixing angles. We show that the Wtb
coupling constraints become relevant if the precision of single top production
cross section measurements could be reduced to 1\% relative to the SM
predictions in future.Comment: Chin. Phys. C in pres

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