26,896 research outputs found
Realization of Artificial Ice Systems for Magnetic Vortices in a Superconducting MoGe Thin-film with Patterned Nanostructures
We report an anomalous matching effect in MoGe thin films containing pairs of
circular holes arranged in such a way that four of those pairs meet at each
vertex point of a square lattice. A remarkably pronounced fractional matching
was observed in the magnetic field dependences of both the resistance and the
critical current. At the half matching field the critical current can be even
higher than that at zero field. This has never been observed before for
vortices in superconductors with pinning arrays. Numerical simulations within
the nonlinear Ginzburg-Landau theory reveal a square vortex ice configuration
in the ground state at the half matching field and demonstrate similar
characteristic features in the field dependence of the critical current,
confirming the experimental realization of an artificial ice system for
vortices for the first time.Comment: To appear in Phys. Rev. Let
Analysis of Y(4660) and related bound states with QCD sum rules
In this article, we take the vector charmonium-like state Y(4660) as a
bound state (irrespective of the hadro-charmonium and the
molecular state) tentatively, study its mass using the QCD sum rules, the
numerical value is consistent with the experimental
data. Considering the SU(3) symmetry of the light flavor quarks and the heavy
quark symmetry, we also study the bound states ,
and with the QCD sum rules,
and make reasonable predictions for their masses.Comment: 18 pages, 32 figures, revised versio
Edge and Bulk Transport in the Mixed State of a Type-II Superconductor
By comparing the voltage-current (V-I) curves obtained before and after
cutting a sample of 2H-NbSe2, we separate the bulk and edge contributions to
the transport current at various dissipation levels and derive their respective
V- I curves and critical currents. We find that the edge contribution is
thermally activated across a current dependent surface barrier. By contrast the
bulk V-I curves are linear, as expected from the free flux flow model. The
relative importance of bulk and edge contributions is found to depend on
dissipation level and sample dimensions. We further show that the peak effect
is a sharp bulk phenomenon and that it is broadened by the edge contribution
Stop reasoning! When multimodal LLMs with chain-of-thought reasoning meets adversarial images
Recently, Multimodal LLMs (MLLMs) have
shown a great ability to understand images. However, like traditional vision models, they are
still vulnerable to adversarial images. Meanwhile, Chain-of-Thought (CoT) reasoning has
been widely explored on MLLMs, which not only
improves model’s performance, but also enhances
model’s explainability by giving intermediate reasoning steps. Nevertheless, there is still a lack
of study regarding MLLMs’ adversarial robustness with CoT and an understanding of what the
rationale looks like when MLLMs infer wrong
answers with adversarial images. Our research
evaluates the adversarial robustness of MLLMs
when employing CoT reasoning, finding that
CoT marginally improves adversarial robustness
against existing attack methods. Moreover, we
introduce a novel stop-reasoning attack technique
that effectively bypasses the CoT-induced robustness enhancements. Finally, we demonstrate the
alterations in CoT reasoning when MLLMs confront adversarial images, shedding light on their
reasoning process under adversarial attacks
Correlations among superconductivity, structural instability, and band filling in Nb1-xB2 at the critical point x=0.2
We performed an extensive investigation on the correlations among
superconductivity, structural instability and band filling in Nb1-xB2
materials. Structural measurements reveal that a notable phase transformation
occurs at x=0.2, corresponding to the Fermi level (EF) in the pseudogap with
the minimum total density of states (DOS) as demonstrated by the
first-principles calculations. Superconductivity in Nb1-xB2 generally becomes
visible in the Nb-deficient materials with x=0.2. Electron energy-loss
spectroscopy (EELS) measurements on B K-edge directly demonstrated the presence
of a chemical shift arising from the structural transformation. Our
systematical experimental results in combination with theoretical analysis
suggest that the emergence of hole states in the sigma-bands plays an important
role for understanding the superconductivity and structural transition in
Nb1-xB2.Comment: 16 pages, 4 figure
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