Author Affiliations
Abstract
1 Department of Physics, State Key Laboratory of Surface Physics and Key Laboratory of Micro- and Nano-Photonic Structure (MOE), Fudan University, Shanghai 200433, China.
2 Department of Physics, University of California, Berkeley, Berkeley, CA 94720, USA.
3 School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China.
The surface/interface species in perovskite oxides play essential roles in many novel emergent physical phenomena and chemical processes. With low eigen-energies in the terahertz region, such species at buried interfaces remain poorly understood due to the lack of feasible surface-specific spectroscopic probes to resolve the resonances. Here, we show that polarized phonons and two-dimensional electron gas at the interface can be characterized using surface-specific nonlinear optical spectroscopy in the terahertz range. This technique uses intra-pulse difference frequency mixing process, which is allowed only at the surface/interface of a centrosymmetric medium. Submonolayer sensitivity can be achieved using the state-of-the-art detection scheme for the terahertz emission from the surface/interface. Through symmetry analysis and proper polarization selection, background-free Drude-like nonlinear response from the two-dimensional electron gas emerging at the LaAlO3/SrTiO3 or Al2O3/SrTiO3 interface was successfully observed. The surface/interface potential, which is a key parameter for SrTiO3-based interface superconductivity and photocatalysis, can now be determined optically in a nonvacuum environment via quantitative analysis on the phonon spectrum that was polarized by the surface field in the interfacial region. The interfacial species with resonant frequencies in the THz region revealed by our method provide more insights into the understanding of physical properties of complex oxides.
Ultrafast Science
2023, 3(1): 0042
Sheng Zhang 1,2†Yongwei Cui 1,2,3Shunjia Wang 1,2Haoran Chen 1,2,3[ ... ]Zhensheng Tao 1,2,*
Author Affiliations
Abstract
1 Fudan University, State Key Laboratory of Surface Physics, Department of Physics, Shanghai, China
2 Fudan University, Key Laboratory of Micro and Nano Photonic Structures, Shanghai, China
3 Shanghai Research Center for Quantum Sciences, Shanghai, China
4 Beijing Normal University, Center for Advanced Quantum Studies, Department of Physics, Beijing, China
5 Fudan University, Institute for Nanoelectronic Devices and Quantum Computing, Shanghai, China
Precise and ultrafast control over photo-induced charge currents across nanoscale interfaces could lead to important applications in energy harvesting, ultrafast electronics, and coherent terahertz sources. Recent studies have shown that several relativistic mechanisms, including inverse spin-Hall effect, inverse Rashba–Edelstein effect, and inverse spin-orbit-torque effect, can convert longitudinally injected spin-polarized currents from magnetic materials to transverse charge currents, thereby harnessing these currents for terahertz generation. However, these mechanisms typically require external magnetic fields and exhibit limitations in terms of spin-polarization rates and efficiencies of relativistic spin-to-charge conversion. We present a nonrelativistic and nonmagnetic mechanism that directly utilizes the photoexcited high-density charge currents across the interface. We demonstrate that the electrical anisotropy of conductive oxides RuO2 and IrO2 can effectively deflect injected charge currents to the transverse direction, resulting in efficient and broadband terahertz radiation. Importantly, this mechanism has the potential to offer much higher conversion efficiency compared to previous methods, as conductive materials with large electrical anisotropy are readily available, whereas further increasing the spin-Hall angle of heavy-metal materials would be challenging. Our findings offer exciting possibilities for directly utilizing these photoexcited high-density currents across metallic interfaces for ultrafast electronics and terahertz spectroscopy.
terahertz optics ultrafast science nanophotonics 
Advanced Photonics
2023, 5(5): 056006
Author Affiliations
Abstract
Department of Physics, Fudan University, Shanghai 200438, China
Measuring magnetic response from spin and current is of fundamental interest in condensed matter physics. Negatively charged nitrogen-vacancy (NV-) centers in diamond are emerging as a robust and versatile quantum sensor owing to their high sensitivity, nanometer-scale spatial resolution, and noninvasive operation with access to static and dynamic magnetic and electron transport properties. In this review, we discuss the rapidly growing interest in the implementation of NV- magnetometry to explore condensed matter physics, focusing on three topics: anti/ferromagnetic materials, superconductors, and metals/semimetals/semiconductors.
Photonics Research
2023, 11(3): 393
Author Affiliations
Abstract
State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China
A high-sensitivity DC magneto-optical Kerr effect (MOKE) apparatus is described in this Letter. Via detailed analysis on several dominating noise sources, we have proposed solutions that significantly lower the MOKE noise, and a sensitivity of 1.5×10-7 rad/Hz is achieved with long-term stability. The sensitivity of the apparatus is tested by measuring a wedge-shaped Ni thin film on SiO2 with Ni thickness varying from 0 to 3 nm. A noise floor of 1.5×10-8 rad is demonstrated. The possibility of further improving sensitivity to 10-9 rad via applying AC modulation is also discussed.
high sensitivity direct current magneto-optical Kerr effect 
Chinese Optics Letters
2022, 20(11): 111201
Author Affiliations
Abstract
1 Fudan University, Department of Physics and State Key Laboratory of Surface Physics, Shanghai, China
2 Shanghai Research Center for Quantum Sciences, Shanghai, China
The ability to generate and manipulate broadband chiral terahertz waves is essential for applications in material imaging, terahertz sensing, and diagnosis. It can also open up new possibilities for nonlinear terahertz spectroscopy and coherent control of chiral molecules and magnetic materials. The existing methods, however, often suffer from low efficiency, narrow bandwidth, or poor flexibility. Here, we propose a novel type of laser-driven terahertz emitters, consisting of metasurface-patterned magnetic multilayer heterostructures, that can overcome the shortcomings of the conventional approaches. Such hybrid terahertz emitters combine the advantages of spintronic emitters for being ultrabroadband, efficient, and highly flexible, as well as those of metasurfaces for the powerful control capabilities over the polarization state of emitted terahertz waves on an ultracompact platform. Taking a stripe-patterned metasurface as an example, we demonstrate the efficient generation and manipulation of broadband chiral terahertz waves. The ellipticity can reach >0.75 over a broad terahertz bandwidth (1 to 5 THz), representing a high-quality and efficient source for few-cycle circularly polarized terahertz pulses with stable carrier waveforms. Flexible control of ellipticity and helicity is also demonstrated with our systematic experiments and numerical simulations. We show that the terahertz polarization state is dictated by the interplay between laser-induced spintronic-origin currents and the screening charges/currents in the metasurfaces, which exhibits tailored anisotropic properties due to the predesigned geometric confinement effects. Our work opens a new pathway to metasurface-tailored spintronic emitters for efficient vector-control of electromagnetic waves in the terahertz regime.
chiral terahertz generation active metasurface time-domain terahertz spectroscopy 
Advanced Photonics
2021, 3(5): 056002
作者单位
摘要
1 北京大学
2 复旦大学
光子学报
2021, 50(8): 0850200
作者单位
摘要
复旦大学 物理系,上海200438
甲烷水合物(可燃冰)作为一种储量巨大、分布广泛的清洁能源而备受关注。围绕甲烷水合物的开采、以固态水合物形式储运天然气和氢气等问题开展基础科学研究,具有重要的科学意义和应用价值。成核过程是甲烷水合物形成的关键第一步,由甲烷、水分子形成团簇并逐渐演化形成水合物的微观过程。然而,由于缺乏在高压环境下研究成核微观过程的有效实验方法,针对成核过程的实验研究进展缓慢。本文首先对气体水合物的结构及其性质进行了回顾;然后,以水合物演化的分子动力学模拟为基础,梳理现有关于水合物演化路径的初步认知;最后,以超快非线性光谱学方法为主,讨论了水合物实验研究的进展和展望。
甲烷水合物 分子动力学模拟 拉曼光谱 中子衍射 和频振动光谱 Methane hydrate Molecular dynamics simulation Raman spectroscopy Neutron diffraction Sum frequency vibrational spectroscopy 
光子学报
2021, 50(8): 0850205

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