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1,230 results on '"Ouyang, Xiao"'

6. Switchable polarization manipulation, optical logical gates and conveyor belt based on U-shaped $\ce{VO2}$ nanoholes

Author

Ouyang, Xiao-Yu and Yang, Jing

Subjects
Physics - Optics, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

Based on U-shaped plasmonic nanoholes in an $\ce{Au-VO2-Au}$ film, we propose to achieve several switchable functions at the telecom wavelength by transition from the $\ce{VO2}$ semiconductive state to the metallic state. The first is the polarization manipulation of four different polarization states ($x\&y$-polarization, LCP, and RCP). An array of U-shaped holes constitutes of the high efficiency SPP splitter, and thus the spin-encoded optical logical gates can be achieved. Furthurmore, we prove that a nano-optical conveyor belt can be build up with such U-shaped holes, making the transport of nanoparticles over the film efficiency by transforming between two spin states periodically, and the transport direction switchably along with the $\ce{VO2}$ phase.

Published
2023

8. Complex phase diagram and supercritical matter

Author

Ouyang, Xiao-Yu, Ye, Qi-Jun, and Li, Xin-Zheng

Subjects
Condensed Matter - Statistical Mechanics
Abstract

The supercritical region is often described as uniform with no definite transitions. The distinct behaviors of the matter therein (as liquid-like and gas-like), however, suggest ``supercritical boundaries". Here, we provide a mathematical description of these phenomena by revisiting the Lee-Yang (LY) theory and introducing a complex phase diagram, i.e. a 4-D one with complex $T$ and $p$. While the traditional 2-D phase diagram with real $T$ and $p$ values (the physical plane) lacks LY zeros beyond the critical point, preventing the occurrence of criticality, the off-plane zeros in this 4-D scenario possess critical anomalies in various physical properties. For example, when the isobaric heat capacity $C_p$, which is a response function of the system to $T$, is used to separate the supercritical region, this 4D complex phase diagram can be visualized by reducing to a 3D one with complex $T$ and real $p$. Then, we find that the supercritical boundary defined by $C_p$ shows perfect correspondence with the projection of the edges of the LY zeros with complex $T$ in this 3D phase diagram on the physical plane, whilst in conventional LY theory these off-plane zeros are neglected. The same relation applies to the isothermal compression coefficient $K_T$ (or $\kappa_T$) which is a response function of the system to $p$, where complex $p$ should be used. This correlation between the Widom line and the edges of LY zeros is demonstrated in three systems, i.e., van der Waals model, 2D Ising model and water, which unambiguously reveals the incipient phase transition nature of the supercritical matter. With this extension of the LY theory and the associated new findings, a unified picture of phase and phase transition valid for both the phase transition and supercritical regions is provided, which should apply to the complex phase diagram of other thermodynamic state functions.

Published
2023

35. Breakdown of the Hund's Rule in CuFeAs

Author

Song, Ze-Yi, Jiang, Xiu-Cai, Ouyang, Xiao-Fang, and Zhang, Yu-Zhong

Subjects
Condensed Matter - Superconductivity, Condensed Matter - Strongly Correlated Electrons
Abstract

The ground-state properties of CuFeAs were investigated by applying density functional theory calculations within generalized gradient approximation (GGA) and GGA+U. We find that the bicollinear antiferromagnetic state with antiparallel orbital magnetic moments on each iron which violates the Hund's rule is favored by the on-site Coulomb interaction, which is further stabilized by Cu vacancy. The magnetic ground state can be used to understand weak antiferromagnetism in CuFeAs observed experimentally. We argue that breakdown of the Hund's rule may be the possible origin for reduced magnetism in iron pnictides, rather than magnetic fluctuations induced by electronic correlations., Comment: 8 pages, 5 figures

Published
2021
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