Yang Wang

Peking University

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Chengyin Wu

Shanxi University

Qihuang Gong

Peking University

G. M. Stocks

Oak Ridge National Laboratory

Zenghu Chang

University of Ottawa

Jie Li

Chinese Academy of Sciences

Yanchun Yin

University of Central Florida

Yi Wu

University of Central Florida

Pengzuo Jiang

Peking University

Xiaoming Ren

Earthquake Planning and Protection Organization

David S. Weiss

Pennsylvania State University

Cooperative Institutions

Peking University

Chinese Academy of Sciences

University of Chinese Academy of Sciences

Oak Ridge National Laboratory

University College London

Collaborative Innovation Center of Quantum Matter

RIKEN Nishina Center

University of Central Florida

University of California, Berkeley

Osaka University

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Controlling the polarization of nitrogen ion lasing

arXiv (Cornell University) (2023)

Jingsong Gao Xiang Zhang Yang Wang Jiahao Dong Mingwei Lei

Air lasing provides a promising technique to remotely produce coherent radiation in the atmosphere and attracts continuous attention. However, the polarization properties of N2+ lasing with seeding has not been understood since it was discovered ten years ago, in which the behaviors appear disordered and confusing. Here, we performed an experimental and theoretical investigation on the polarization properties of N2+ lasing and successfully revealed its underlying physical mechanism. We found that the optical gain is anisotropic owing to the permanent alignment of N2+ induced by the preferential ionization of the pump light. As a result, the polarization of N2+ lasing tends to align with that of the pump light after amplification, which becomes more pronounced with increasing amplification factor. Based on the permanent alignment of N2+, we built a theoretical model that analytically interpreted and numerically reproduced the experimental observations, which points out the key factors for controlling the polarization of N2+ lasing.

10.48550/arxiv.2311.01225

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Delving into Discrete Normalizing Flows on SO(3) Manifold for Probabilistic Rotation Modeling

2022 IEEE/CVF Conference on Computer Vision and Pattern Recognition (CVPR) (2023)

Yulin Liu Haoran Liu Yingda Yin Yang Wang Baoquan Chen

Normalizing flows (NFs) provide a powerful tool to construct an expressive distribution by a sequence of trackable transformations of a base distribution and form a probabilistic model of underlying data. Rotation, as an important quantity in computer vision, graphics, and robotics, can exhibit many ambiguities when occlusion and symmetry occur and thus demands such probabilistic models. Though much progress has been made for NFs in Euclidean space, there are no effective normalizing flows without discontinuity or many-to-one mapping tailored for SO(3) manifold. Given the unique non-Euclidean properties of the rotation manifold, adapting the existing NFs to SO(3) manifold is non-trivial. In this paper, we propose a novel normalizing flow on SO (3) by combining a Mobius transformation-based coupling layer and a quaternion affine transformation. With our proposed rotation normalizing flows, one can not only effectively express arbitrary distributions on SO(3), but also conditionally build the target distribution given input observations. Extensive experiments show that our rotation normalizing flows significantly outperform the baselines on both unconditional and conditional tasks.

Manifold (fluid mechanics)

10.1109/cvpr52729.2023.02037

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Effects of strain and defects on the topological properties of HfTe5

Physical review. B./Physical review. B (2024)

Na Hyun Jo Omar A. Ashour Zhixue Shu Chris Jozwiak Aaron Bostwick

Manipulating topological states holds significant interest in the field of condensed matter physics. Here, the authors control the topological phase and corresponding quasiparticle dynamics by managing defects, and further reverse these effects through $i\phantom{\rule{0}{0ex}}n$ $s\phantom{\rule{0}{0ex}}i\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}u$ uniaxial stress control in HfTe${}_{5}$. The findings showcase the potential of employing both defect chemistry and strain engineering as tools to manipulate topological phase transitions and related many-body physics.

Topological defect

10.1103/physrevb.109.235122

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Developing Ni single-atom sites in carbon nitride for efficient photocatalytic H2O2 production

Nature Communications (2023)

Xu Zhang Hui Su Peixin Cui Yongyong Cao Zhenyuan Teng

Photocatalytic two-electron oxygen reduction to produce high-value hydrogen peroxide (H2O2) is gaining popularity as a promising avenue of research. However, structural evolution mechanisms of catalytically active sites in the entire photosynthetic H2O2 system remains unclear and seriously hinders the development of highly-active and stable H2O2 photocatalysts. Herein, we report a high-loading Ni single-atom photocatalyst for efficient H2O2 synthesis in pure water, achieving an apparent quantum yield of 10.9% at 420 nm and a solar-to-chemical conversion efficiency of 0.82%. Importantly, using in situ synchrotron X-ray absorption spectroscopy and Raman spectroscopy we directly observe that initial Ni-N3 sites dynamically transform into high-valent O1-Ni-N2 sites after O2 adsorption and further evolve to form a key *OOH intermediate before finally forming HOO-Ni-N2. Theoretical calculations and experiments further reveal that the evolution of the active sites structure reduces the formation energy barrier of *OOH and suppresses the O=O bond dissociation, leading to improved H2O2 production activity and selectivity.

Quantum yield

Oxygen evolution

10.1038/s41467-023-42887-y

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Citations (165)

Ultrafast Electron Dynamics Dominated by Electron–Phonon Coupling in CrSBr Revealed by Photoemission Electron Microscopy

The Journal of Physical Chemistry C (2024)

Pengzuo Jiang Yaolong Li Xiaying Lyu Jingying Xiao Xiaofang Li

Layered semiconductor CrSBr has drawn much attention due to its two-dimensional magnetic orders and strong multiphysics couplings. Herein, the electron dynamics of CrSBr (few layers to tens of nanometers) is investigated by time-resolved photoemission electron microscopy with various photoexciting conditions. The valence electrons around the Γ point are considered to be excited along the Γ-Y direction and scattered with phonons along the nearly flat conduction band in the Γ-X direction. The relaxation lifetime of photoelectrons decreases from ∼11 ps at 100 K to ∼2 ps at room temperature, presenting strong electron–phonon coupling in CrSBr. The lifetime is also found to be independent of pump polarization, which implies that the excited-state electrons follow the identical relaxation channel, although CrSBr possesses great anisotropy.

10.1021/acs.jpcc.4c07231

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Spectroscopic Evidence for a Three-Dimensional Charge Density Wave in Kagome Superconductor CsV$_3$Sb$_5$

Research Square (Research Square) (2021)

Cong Li Xianxin Wu Hongxiong Liu Craig Polley Qinda Guo

The recently discovered AV3Sb5 (A=K, Rb, Cs) family, possessing V kagome nets, has received considerable attention due to the topological electronic structure and intriguing correlated phenomena, including an exotic charge density wave (CDW) and superconductivity. Detailed electronic structure studies are essential to unravel the characteristics and origin of the CDW as well as its interplay with superconductivity. Here, we present angle-resolved photoemission spectroscopy (ARPES) measurements for CsV3Sb5 at multiple temperatures and photon energies to reveal the nature of the CDW from an electronic structure perspective. We present evidence for a three-dimensional (3D) CDW order. In the process we also pinpoint a surface state attributed to a Cs terminated surface. This state was previously attributed to band folding band due to a CDW along the c direction or a quantum well state from quantum confinement. The CDW expected 2-fold lattice reconstruction along c axis is observed to be a quadrupling of the unit cell, thus for the first time directly demonstrating the 3D nature of the CDW from the electronic structure perspective. Moreover, this 3D CDW configuration originates from two distinct types of distortions in adjacent kagome layers. These present results not only provide key insights into the nature of the unconventional CDW in CsV3Sb5 but also provides an important reference for further studies on the relationship between the CDW and superconductivity.

Charge Density Wave

Lattice (music)

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Single and pair-wise manipulation of atoms in a 3D optical lattice

Bulletin of the American Physical Society (2013)

Theodore A. Corcovilos Yang Wang David S. Weiss

Lattice (music)

Optical lattice

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The Fast Multipole Method for 2D Coulombic Problems: Analysis, Implementation and Visualization

Yang Wang

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Citations (2)

Green Function Calculation for Full-potential Multiple Scattering Methods

APS March Meeting Abstracts (2001)

Yang Wang G. M. Stocks Don M. Nicholson

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Attosecond light sources in the water window

Journal of Optics (2017)

Xiaoming Ren Jie Li Yanchun Yin Kun Zhao Andrew Chew

As a compact and burgeoning alternative to synchrotron radiation and free-electron lasers, high harmonic generation (HHG) has proven its superiority in static and time-resolved extreme ultraviolet spectroscopy for the past two decades and has recently gained many interests and successes in generating soft x-ray emissions covering the biologically important water window spectral region. Unlike synchrotron and free-electron sources, which suffer from relatively long pulse width or large time jitter, soft x-ray sources from HHG could offer attosecond time resolution and be synchronized with their driving field to investigate time-resolved near edge absorption spectroscopy, which could reveal rich structural and dynamical information of the interrogated samples. In this paper, we review recent progresses on generating and characterizing attosecond light sources in the water window region. We show our development of an energetic, two-cycle, carrier-envelope phase stable laser source at 1.7 μm and our achievement in producing a 53 as soft x-ray pulse covering the carbon K-edge in the water window. Such source paves the ways for the next generation x-ray spectroscopy with unprecedented temporal resolution.

Water window

Attosecond

Extreme ultraviolet

10.1088/2040-8986/aaa394

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Citations (73)