94,958 research outputs found
Superconducting pairing of interacting electrons: implications from the two-impurity Anderson model
We study the non-local superconducting pairing of two interacting Anderson
impurities, which has an instability near the quantum critical point from the
competition between the Kondo effect and an antiferromagnetic inter-impurity
spin exchange interaction. As revealed by the dynamics over the whole energy
range, the superconducting pairing fluctuations acquire considerable strength
from an energy scale much higher than the characteristic spin fluctuation scale
while the low energy behaviors follow those of the staggered spin
susceptibility. We argue that the glue to the superconducting pairing is not
the spin fluctuations, but rather the effective Coulomb interaction. On the
other hand, critical spin fluctuations in the vicinity of quantum criticality
are also crucial to a superconducting pairing instability, by preventing a
Fermi liquid fixed point being reached to keep the superconducting pairing
fluctuations finite at low energies. A superconducting order, to reduce the
accumulated entropy carried by the critical degrees of freedom, may arise
favorably from this instability.Comment: 6 pages, 2 figure
Spin-dependent Fano resonance induced by conducting chiral helimagnet contained in a quasi-one-dimensional electron waveguide
Fano resonance appears for conduction through an electron waveguide
containing donor impurities. In this work, we consider the thin-film conducting
chiral helimagnet (CCH) as the donor impurity in a one-dimensional waveguide
model. Due to the spin spiral coupling, interference between the direct and
intersubband transmission channels gives rise to spin-dependent Fano resonance
effect. The spin-dependent Fano resonance is sensitively dependent on the
helicity of the spiral. By tuning the CCH potential well depth and the incident
energy, this provides a potential way to detect the spin structure in the CCH.Comment: 14 pages, 6 figure
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Lateral shearing interferometry for high-NA EUV wavefront metrology
We present a lateral shearing interferometer suitable for high-NA EUV wavefront metrology. In this interferometer, a geometric model is used to accurately characterize and predict systematic errors that come from performing interferometry at high NA. This interferometer is compatible with various optical geometries, including systems where the image plane is tilted with respect to the optical axis, as in the Berkeley MET5. Simulation results show that the systematic errors in tilted geometries can be reduced by aligning the shearing interferometer grating and detector parallel to the image plane. Subsequent residual errors can be removed by linear fitting
Dynamic microscopic structures and dielectric response in the cubic-to-tetragonal phase transition for BaTiO3 studied by first-principles molecular dynamics simulation
The dynamic structures of the cubic and tetragonal phase in BaTiO3 and its
dielectric response above the cubic-to-tetragonal phase transition temperature
(Tp) are studied by first-principles molecular dynamics (MD) simulation. It's
shown that the phase transition is due to the condensation of one of the
transverse correlations. Calculation of the phonon properties for both the
cubic and tetragonal phase shows a saturation of the soft mode frequency near
60 cm-1 near Tp and advocates its order-disorder nature. Our first-principles
calculation leads directly to a two modes feature of the dielectric function
above Tp [Phys. Rev. B 28, 6097 (1983)], which well explains the long time
controversies between experiments and theories
Redistribution of phase fluctuations in a periodically driven cuprate superconductor
We study the thermally fluctuating state of a bi-layer cuprate superconductor
under the periodic action of a staggered field oscillating at optical
frequencies. This analysis distills essential elements of the recently
discovered phenomenon of light enhanced coherence in YBaCuO,
which was achieved by periodically driving infrared active apical oxygen
distortions. The effect of a staggered periodic perturbation is studied using a
Langevin and Fokker-Planck description of driven, coupled Josephson junctions,
which represent two neighboring pairs of layers and their two plasmons. In a
toy model including only two junctions, we demonstrate that the external
driving leads to a suppression of phase fluctuations of the low-energy plasmon,
an effect which is amplified via the resonance of the high energy plasmon. When
extending the modeling to the full layers, we find that this reduction becomes
far more pronounced, with a striking suppression of the low-energy
fluctuations, as visible in the power spectrum. We also find that this effect
acts onto the in-plane fluctuations, which are reduced on long length scales.
All these findings provide a physical framework to describe light control in
cuprates
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