5,088 research outputs found
Hybridization-driven gap in U3Bi4Ni3: a 209Bi NMR/NQR study
We report 209Bi NMR and NQR measurements on a single crystal of the Kondo
insulator U3Bi4Ni3. The 209Bi nuclear spin-lattice relaxation rate ()
shows activated behavior and is well-fit by a spin gap of 220 K. The 209Bi
Knight shift (K) exhibits a strong temperature dependence arising from 5f
electrons, in which K is negative at high temperatures and increases as the
temperature is lowered. Below 50 K, K shows a broad maximum and decreases
slightly upon further cooling. Our data provide insight into the evolution of
the hyperfine fields in a fully gapped Kondo insulator based on 5f electron
hybridization.Comment: 4 pages, 4 figures, submitted to Phys. Rev.
Uncovering the Hidden Order in URu2Si2 by Impurity Doping
We report the use of impurities to probe the hidden order parameter of the
strongly correlated metal URu_2Si_2 below the transition temperature T_0 ~ 17.5
K. The nature of this order parameter has eluded researchers for more than two
decades, but is accompanied by the development of a partial gap in the single
particle density of states that can be detected through measurements of the
electronic specific heat and nuclear spin-lattice relaxation rate. We find that
impurities in the hidden order phase give rise to local patches of
antiferromagnetism. An analysis of the coupling between the antiferromagnetism
and the hidden order reveals that the former is not a competing order parameter
but rather a parasitic effect of the latter.Comment: 4 pages, 4 figure
Production and detection of doubly charmed tetraquarks
The feasibility of tetraquark detection is studied. For the cc\bar{u}\bar{d}
tetraquark we show that in present (SELEX, Tevatron, RHIC) and future
facilities (LHCb, ALICE) the production rate is promising and we propose some
detectable decay channels.Comment: 6 pages, 5 figure
A Quasi-Conforming Embedded Reproducing Kernel Particle Method for Heterogeneous Materials
We present a quasi-conforming embedded reproducing kernel particle method
(QCE-RKPM) for modeling heterogeneous materials that makes use of techniques
not available to mesh-based methods such as the finite element method (FEM) and
avoids many of the drawbacks in current embedded and immersed formulations
which are based on meshed methods. The different material domains are
discretized independently thus avoiding time-consuming, conformal meshing. In
this approach, the superposition of foreground (inclusion) and background
(matrix) domain integration smoothing cells are corrected by a quasi-conforming
quadtree subdivision on the background integration smoothing cells. Due to the
non-conforming nature of the background integration smoothing cells near the
material interfaces, a variationally consistent (VC) correction for domain
integration is introduced to restore integration constraints and thus optimal
convergence rates at a minor computational cost. Additional interface
integration smoothing cells with area (volume) correction, while
non-conforming, can be easily introduced to further enhance the accuracy and
stability of the Galerkin solution using VC integration on non-conforming
cells. To properly approximate the weak discontinuity across the material
interface by a penalty-free Nitsche's method with enhanced coercivity, the
interface nodes on the surface of the foreground discretization are also shared
with the background discretization. As such, there are no tunable parameters,
such as those involved in the penalty type method, to enforce interface
compatibility in this approach. The advantage of this meshfree formulation is
that it avoids many of the instabilities in mesh-based immersed and embedded
methods. The effectiveness of QCE-RKPM is illustrated with several examples
Practical long-distance quantum key distribution system using decoy levels
Quantum key distribution (QKD) has the potential for widespread real-world
applications. To date no secure long-distance experiment has demonstrated the
truly practical operation needed to move QKD from the laboratory to the real
world due largely to limitations in synchronization and poor detector
performance. Here we report results obtained using a fully automated, robust
QKD system based on the Bennett Brassard 1984 protocol (BB84) with low-noise
superconducting nanowire single-photon detectors (SNSPDs) and decoy levels.
Secret key is produced with unconditional security over a record 144.3 km of
optical fibre, an increase of more than a factor of five compared to the
previous record for unconditionally secure key generation in a practical QKD
system.Comment: 9 page
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