4,599 research outputs found
Anisotropic Dirac fermions in a Bi square net of SrMnBi2
We report the highly anisotropic Dirac fermions in a Bi square net of
SrMnBi2, based on a first principle calculation, angle resolved photoemission
spectroscopy, and quantum oscillations for high-quality single crystals. We
found that the Dirac dispersion is generally induced in the (SrBi)+ layer
containing a double-sized Bi square net. In contrast to the commonly observed
isotropic Dirac cone, the Dirac cone in SrMnBi2 is highly anisotropic with a
large momentum-dependent disparity of Fermi velocities of ~ 8. These findings
demonstrate that a Bi square net, a common building block of various layered
pnictides, provide a new platform that hosts highly anisotropic Dirac fermions.Comment: 5 pages, 4 figure
Unveiling the ac Dynamics of Ferroelectric Domains by Investigating the Frequency Dependence of Hysteresis Loops
We investigated nonequilibrium domain wall dynamics under an ac field by
measuring the hysteresis loops of epitaxial ferroelectric capacitors at various
frequencies and temperatures. Polarization switching is induced mostly by
thermally activated creep motion at lower frequencies, and by viscous flow
motion at higher frequencies. The dynamic crossover between the creep and flow
regimes unveils two frequency-dependent scaling regions of hysteresis loops.
Based on these findings, we constructed a dynamic phase diagram for hysteretic
ferroelectric domain dynamics in the presence of ac fields.Comment: 3 figure
Gaussian Quantum Illumination via Monotone Metrics
Quantum illumination is to discern the presence or absence of a low
reflectivity target, where the error probability decays exponentially in the
number of copies used. When the target reflectivity is small so that it is hard
to distinguish target presence or absence, the exponential decay constant falls
into a class of objects called monotone metrics. We evaluate monotone metrics
restricted to Gaussian states in terms of first-order moments and covariance
matrix. Under the assumption of a low reflectivity target, we explicitly derive
analytic formulae for decay constant of an arbitrary Gaussian input state.
Especially, in the limit of large background noise and low reflectivity, there
is no need of symplectic diagonalization which usually complicates the
computation of decay constants. First, we show that two-mode squeezed vacuum
(TMSV) states are the optimal probe among pure Gaussian states with fixed
signal mean photon number. Second, as an alternative to preparing TMSV states
with high mean photon number, we show that preparing a TMSV state with low mean
photon number and displacing the signal mode is a more experimentally feasible
setup without degrading the performance that much. Third, we show that it is of
utmost importance to prepare an efficient idler memory to beat coherent states
and provide analytic bounds on the idler memory transmittivity in terms of
signal power, background noise, and idler memory noise. Finally, we identify
the region of physically possible correlations between the signal and idler
modes that can beat coherent states.Comment: 16 pages, 6 figure
Multiferroic properties of epitaxially stabilized hexagonal DyMnO3 thin films
We fabricated epitaxial thin films of hexagonal DyMnO3, which otherwise form
in a bulk perovskite structure, via deposition on Pt(111)//Al2O3 (0001) and
YSZ(111) substrates: each of which has in-plane hexagonal symmetry. The
polarization hysteresis loop demonstrated the existence of ferroelectricity in
our hexagonal DyMnO3 films at least below 70 K. The observed 2.2 uC/cm^2
remnant polarization at 25 K corresponded to a polarization enhancement by a
factor of 10 compared to that of the bulk orthorhombic DyMnO3. Interestingly,
this system showed an antiferroelectric-like feature in its hysteresis loop.
Our hexagonal DyMnO3 films showed an antiferromagnetic Neel temperature around
60 K and a spin reorientation transition around 40 K. We also found a clear
hysteresis in the temperature dependence of the magnetization, which was
measured after zero-field-cooling and field-cooling. This hysteresis may well
have been of spin glass origin, which was likely to arise from the geometric
frustration of antiferromagnetically-coupled Mn spins with an edge-sharing
triangular lattice
Lowering the energy threshold in COSINE-100 dark matter searches
COSINE-100 is a dark matter detection experiment that uses NaI(Tl) crystal
detectors operating at the Yangyang underground laboratory in Korea since
September 2016. Its main goal is to test the annual modulation observed by the
DAMA/LIBRA experiment with the same target medium. Recently DAMA/LIBRA has
released data with an energy threshold lowered to 1 keV, and the persistent
annual modulation behavior is still observed at 9.5. By lowering the
energy threshold for electron recoils to 1 keV, COSINE-100 annual modulation
results can be compared to those of DAMA/LIBRA in a model-independent way.
Additionally, the event selection methods provide an access to a few to sub-GeV
dark matter particles using constant rate studies. In this article, we discuss
the COSINE-100 event selection algorithm, its validation, and efficiencies near
the threshold
- …