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Pengfei Zhang

Publications and source records attributed to Pengfei Zhang.

348 records · Page 20Linked to original sources
arXiv2012

Superconductivity in a single layer alkali-doped FeSe: a weakly coupled two-leg ladder system

We prepare single layer potassium-doped iron selenide (110) film by molecular beam expitaxy. Such a single layer film can be viewed as a two-dimensional system composed of weakly coupled two-leg iron ladders. Scanning tunneling spectroscopy reveals that superconductivity is developed in this two-leg ladder system. The superconducting gap is similar to that of the multi-layer films. However, the Fermi surface topology given by first-principles calculation is remarkably different from that of the bulk materials. Our results suggest that superconducting pairing is very short-ranged or takes place rather locally in iron-chalcogenides. The superconductivity is most likely driven by electron-electron correlation effect and is insensitive to the change of Fermi surfaces.

cond-mat.supr-con↗
arXiv2012

Fundamental domain of invariant sets and applications

Let $X$ be a compact metric space and $f:X\to X$ a homeomorphism on $X$. We construct a fundamental domain for the set with finite peaks for each cocycle induced by $ϕ\in C(X,R)$. In particular we prove that if a partially hyperbolic diffeomorphism is accessible, then either the set with finite peaks for the Jacobian cocycle is of full volume, or the set of transitive points is of positive volume.

math.DS↗
arXiv2010

Elimination of degenerate trajectory of single atom strongly coupled to the tilted cavity TEM10 mode

We demonstrate the trajectory measurement of the single neutral atoms deterministically using a high-finesse optical micro-cavity. Single atom strongly couples to the high-order transverse vacuum TEM_{10} mode, instead of the usual TEM_{00} mode, and the parameter of the system is (g_{10},κ,γ)=2π\times (20.5,2.6,2.6)MHz. The atoms simply fall down freely from the magneto-optic trap into the cavity modes and the trajectories of the single atoms are linear. The transmission spectrums of atoms passing through the TEM10 mode are detected by a single photon counting modules and well fitted. Thanks to the tilted cavity transverse TEM10 mode, which is inclined to the vertical direction about 45 degrees and it helps us, for the first time, to eliminate the degenerate trajectory of the single atom falling through the cavity and get the unique atom trajectory. Atom position with high precision of 0.1μm in the off-axis direction (axis y) is obtained, and the spatial resolution of 5.6μm is achieved in time of 10μs along the vertical direction (axis x). The average velocity of the atoms is also measured from the atom transits, which determines the temperature of the atoms in magneto-optic trap, 186μK {\pm} 19μK.

quant-ph↗
arXiv2010

Partially hyperbolic sets with positive measure and $ACIP$ for partially hyperbolic systems

In [Discrete Contin. Dyn. Syst. \textbf{15} (2006), no. 3, 811--818.] Xia introduced a simple dynamical density basis for partially hyperbolic sets of volume preserving diffeomorphisms. We apply the density basis to the study of the topological structure of partially hyperbolic sets. We show that if $Λ$ is a strongly partially hyperbolic set with positive volume, then $Λ$ contains the global stable manifolds over $α(Λ^d)$ and the global unstable manifolds over $ω(Λ^d)$. We give several applications of the dynamical density to partially hyperbolic maps that preserve some $acip$. We show that if $f$ is essentially accessible and $μ$ is an $acip$ of $f$, then $\text{supp}(μ)=M$, the map $f$ is transitive, and $μ$-a.e. $x\in M$ has a dense orbit in $M$. Moreover if $f$ is accessible and center bunched, then either $f$ preserves a smooth measure or there is no $acip$ of $f$.

math.DS↗
arXiv2009

Segmentation for radar images based on active contour

We exam various geometric active contour methods for radar image segmentation. Due to special properties of radar images, we propose our new model based on modified Chan-Vese functional. Our method is efficient in separating non-meteorological noises from meteorological images.

cs.CV↗