基于超快电子自旋动力学的太赫兹辐射研究进展

回顾了近年来利用超快自旋动力学过程产生太赫兹(THz)辐射的研究进展。介绍了基于逆自旋霍尔效应和逆Rashba-Edelstein效应的瞬态自旋流-电荷流转换,指出铁磁/非磁性异质结构已被用于设计低成本、高效率的THz辐射源。通过优化膜厚、生长条件、衬底和结构,可进一步提高基于自旋电子学的THz发射器的效率和带宽。简述了THz发射光谱在研究超快自旋泽贝克效应形成动力学中的应用。     

超快强激光泵浦强太赫兹源及其驱动的材料非平衡态研究进展

太赫兹源是太赫兹科学技术发展和相关应用研究的基础。超快激光为太赫兹的产生和探测提供了稳定、可靠的激发光源。超快激光泵浦各种激发介质可以产生太赫兹波,激发介质主要有4类：1）固体介质,如光电导天线、晶体等;2）气体介质,如空气;3）液体介质,如液态水、液态镓、液氮等;4）等离子体介质,如钛薄膜、金属铜箔。太赫兹场强的进一步提高催生了人们对强场太赫兹与物质的相互作用以及太赫兹非线性光谱学的研究,太赫兹不仅能作为探测物性的手段,其发射光谱亦可以实现对材料中非平衡态载流子与晶格、自旋等有序度的强耦合。本文综述了超快激光激发数种不同类型介质产生太赫兹源的国内外研究发展历程,包括其工作原理以及目前存在的问题,总结了目前强场太赫兹波在物态调控方面的应用,以及太赫兹时间分辨光谱在新型物态探测方面的应用,最后展望了太赫兹源未来的发展趋势和应用前景。     

基于激光成丝的太赫兹时域光谱系统研究综述

太赫兹时域光谱(THz-TDS)技术是一种使用相干探测的频谱分析手段。THz-TDS系统集太赫兹波发射器与探测器于一体,通过相干探测,可以同时获取太赫兹脉冲的电场强度和相位信息,广泛用于生物、材料、安检等领域。超快激光成丝产生太赫兹波是当前产生宽频谱、高强度太赫兹辐射的一个重要途径。文章详细介绍了超快激光成丝辐射太赫兹波的主流物理机制以及增强、调控太赫兹波的主要方法,阐述了基于激光成丝的THz-TDS系统的探测原理和探测手段。     

基于光学技术的太赫兹相干辐射源研究

由于太赫兹辐射的独特性质和潜在的应用价值, 国内外关于太赫兹波的产生和探测的研究正呈现日益繁荣的景象, 目前太赫兹相干辐射源的研究已成为太赫兹技术领域最重要的前沿课题之一。介绍了产生太赫兹相干辐射的三种主要途径：一是光学技术, 它从高频向低频发展, 其代表为太赫兹激光器, 如气体激光器、半导体激光器和量子级联激光器等; 二是电子学技术, 它由低频向高频发展, 如微波管、固体微波源等; 三是光电子技术, 其频率由1 THz向两侧展宽, 采用超快激光脉冲触发产生太赫兹脉冲。设计了基于光学技术的太赫兹相干辐射系统, 该装置根据气体振转能级跃迁原理, 采用高压直流激励方式产生受激辐射, 波导管谐振腔体, 工作气体为N2, CD4和D2, 经过优化设计, 预计可以产生1.54 THz和1.58 THz的波连续输出。     

太赫兹辐射源的研究进展

太赫兹技术在物理、化学等基础研究学科,以及安全检查、空间通信等应用学科都具有重要的研究价值和应用前景,而太赫兹辐射源正是太赫兹技术发展的关键部分.概述了基于激光光学技术、真空电子技术和超快激光技术产生太赫兹辐射的常用方法和主要特点,以及目前的研究状况,并对这各种太赫兹波辐射源的发展方向进行了展望.     

太赫兹超材料和超表面器件的研发与应用

太赫兹光电子学的兴起推动了太赫兹波产生、传输和探测3方面理论和器件的快速发展。通过调控亚波长金属结构与太赫兹波相互作用的特异光学响应,太赫兹超材料和超表面器件已在太赫兹光束整形、导波和调制方面显示了巨大的潜力和优势,并可能推动太赫兹光源和探测器的发展。进一步发展和丰富太赫兹超材料和超表面器件,也将对太赫兹波在传感、通信和雷达等应用方面产生有益影响。本文综述了首都师范大学超材料与器件课题组近年来在太赫兹波段开展的基于超材料和超表面材料的光谱调制器件、光场调制衍射光学元件和主动光学元件的工作,介绍了超材料与器件的基本物理理论以及相应的实验研究成果,希望能够推动超材料与超表面太赫兹调制器件的发展与应用。     

稀土正铁氧体晶体的太赫兹光学调控研究

正交钙钛矿结构RFeO₃系列稀土正铁氧体材料是一类在近红外波段透明的铁磁材料,关于RFeO₃的超快自旋重取向及其相干控制的研究近年来成为相关领域的研究热点。由于固态材料的磁化振子和电子自旋共振能谱等基本性质的“元激发”能量均在太赫兹能量范围内,得益于太赫兹技术的发展,近年来利用太赫兹超快光学调控RFeO₃晶体中不同离子间的交换相互作用、磁各向异性自旋-声子耦合等也取得了一系列突破,对磁学的基础研究具有重要意义。结合笔者近几年的研究进展,总结了国内外RFeO₃晶体太赫兹光学调控研究情况,并对该类晶体的超快光磁研究进行了展望。     

物理所等在Pt薄膜磁近邻效应研究中取得新进展

<正>自旋电子学的发展依赖于对电子自旋状态进行有效调控。除传统的磁场调控手段外,自旋极化电流、自旋流产生的自旋转移力矩效应是对自旋电子材料的自旋动力学行为进行调控的重要手段,尤其是后者,因为不产生焦耳热,是发展未来自旋电子器件的关键技术之一。纯自旋流无法直接通过电测量方式探测,但在非磁材料中的纯自旋流由于自旋-轨道作用,在垂直于自旋     

机器学习辅助太赫兹涡旋波超表面快速设计方法

太赫兹涡旋波产生与调控被认为是6G通信、雷达探测、新型传感器的关键技术之一。利用人工超表面产生涡旋波,相较于传统方法具有平面化、集成化、低成本的特点,但是面临复杂的参数设计和分析,需要耗费大量的时间和算力。为此,提出一种机器学习辅助太赫兹涡旋波超表面快速设计方法,通过长短期记忆(Long Short-Term Memory, LSTM)神经网络法快速得到满足相位需求的超单元并进行一体化组阵。利用该方法,设计构筑了三块模数l分别为1、2、3的太赫兹涡旋波超表面,仿真结果表明,设计的太赫兹涡旋波束模式纯度达到80%以上。机器学习辅助太赫兹涡旋波超表面设计方法具备精度高、快速、一体化设计等优点,有望运用于太赫兹幅度、相位、极化、轨道角动量等复杂波束调控领域。     

自旋电子学研究进展

自旋电子学是上世纪 90年代以来飞速发展起来的新兴学科。与传统的半导体电子器件相比 ,自旋电子器件具有非挥发性、低功耗和高集成度等优点。电子学、光学和磁学的融合发展更有望产生出自旋场效应晶体管、自旋发光二极管、自旋共振隧道器件、THz频率光学开关、调制器、编码器、解码器及用于量子计算、量子通信等装置的新型器件 ,从而触发一场信息技术革命。文中介绍了自旋电子学的若干最新研究进展。     

Strain-Controlled Spin Wave Excitation and Gilbert Damping in Flexible Co2FeSi Films Activated by Femtosecond Laser Pulse

The dynamic response of magnetic order to optical excitation at sub-picosecond scale has offered an intriguing alternative for magnetism manipulation. Such ultrafast optical manipulation of magnetism has become a fundamental challenging topic with high implications for future spintronics. Here, this study demonstrates such manipulation in Co₂FeSi films grown on flexible polyimide substrate, and demonstrates how the magneto-optical interaction can be modified by using strain engineering which in turn triggers the excitation of both dipolar and exchange spin waves modes. Furthermore, Gilbert damping and spin-orbit coupling in Co₂FeSi can both be tuned significantly by altering the magnitude and type of applied strain, suggesting an appealing way to manipulate spin wave propagation. These results develop the optical manipulation magnetism into the field of spin wave dynamics, and open a new direction in the application of spin orbitronics and magnonics devices using strain engineering.     

Compensated Ferrimagnet Based Artificial Synapse and Neuron for Ultrafast Neuromorphic Computing

Spintronic devices are considered a possible solution for the hardware implementation of artificial synapses and neurons, as a result of their non-volatility, high scalability, complementary metal-oxide-semiconductor transistor compatibility, and low power consumption. As compared to ferromagnets, ferrimagnet-based spintronics exhibits equivalently fascinating properties that have been witnessed in ultrafast spin dynamics, together with efficient electrical or optical manipulation. Their applications in neuromorphic computing, however, have still not been revealed, which motivates the present experimental study. Here, by using compensated ferrimagnets containing Co_0.80Gd_0.20 with perpendicular magnetic anisotropy, it is demonstrated that the behavior of spin-orbit torque switching in compensated ferrimagnets could be used to mimic biological synapses and neurons. In particular, by using the anomalous Hall effect and magneto-optical Kerr effect imaging measurements, the ultrafast stimulation of artificial synapses and neurons is illustrated, with a time scale down to 10 ns. Using experimentally derived device parameters, a three-layer fully connected neural network for handwritten digits recognition is further simulated, based on which, an accuracy of more than 93% could be achieved. The results identify compensated ferrimagnets as an intriguing candidate for the ultrafast neuromorphic spintronics.     

Ultrastrong Magnon–Magnon Coupling and Chirality Switching in Antiferromagnet CrPS4

As new information carriers, antiferromagnetic magnons have great potential in the fields of spintronics and quantum information. However, the strong exchange interaction between sublattice spins in conventional antiferromagnets results in their frequencies up to the terahertz (THz) range, hindering further exploration of related applications and physics. Recently, emerging van der Waals A-type antiferromagnets with the weak exchange interaction may bring about a change. In this study, it demonstrates two distinct tunable ultrastrong magnon–magnon couplings in the gigahertz (GHz) band using this type of antiferromagnet, CrPS₄, with a maximum normalized coupling strength (η) of 0.31. It establishes orthorhombic and monoclinic models for theoretical analyses, unambiguously showing that the ultrastrong coupling strength is caused by unique magnetocrystalline anisotropy rather than exchange enhancement. Furthermore, for the first time, it observes a continuous switching process of sublattice magnon chirality arising from the orthorhombic nature of anisotropy. These findings not only deepen the understanding of antiferromagnetic spin dynamics but also offer a powerful platform for building magnonic quantum systems and chirality-based spintronics.     

基于超快激光技术的THz波产生和探测

主要介绍利用超快激光技术产生和探测THz波辐射。THz波探测方法包括电光取样和空气探测。电光取样利用光学电光效应,采用探测激光偏振态的改变得到THz电场时域波形,广泛应用在TDS系统中。空气探测方法利用激光在空气中的三阶非线性效应,可以测得THz时域波形,并且该方法没有晶体的限制,因此可以探测频谱较宽的THz脉冲。产生THz的方法主要包括光电导天线、光学Dember效应、光整流和激光等离子体。其中前三者受到材料本征声子的影响,产生的THz谱宽有一定限制。倾斜激光脉冲波前入射非线性晶体光整流可以产生很强的THz波。双色飞秒激光脉冲与空气等离子体作用,可以产生较强的宽谱THz辐射,并且其谱宽与激光脉冲宽度密切相关。     

A Novel Method of All‐Optical Switching: Quantum Router

Subpicosecond all‐optical switching method based on the simultaneous two‐photon coherence exchange is proposed and numerically demonstrated. The optical switching mechanism is based on the optical field induced dark resonance swapping via nondegenerate four‐wave mixing processes. For potential applications of ultrafast all‐optical switching in fiber‐optic communications, 10‐THz channel number independent quantum router is discussed.     

基于非线性光学差频及参量效应的太赫兹源

基于非线性光学技术的THz源具有其独特的性能和优点,将基于非线性光学差频原理和光学参量效应,从理论上研究并分析THz波与抽运光、闲频光及相位匹配角之间的关系,得到THz波输出的条件和范围,并设计出宽波段连续可调的THz源。以调QNd∶YAG激光器和光学参量振荡器(OPO)作为抽运源,以GaSe和MgO∶LiNbO3晶体作为差频非线性晶体,根据相位匹配理论及光学参量效应,搭建两套THz波产生系统。其中,基于光学参量效应的THz辐射源有效地产生出THz信号。     

A Strain‐Mediated Magnetoelectric‐Spin‐Torque Hybrid Structure

Magnetization dynamics induced by spin–orbit torques in a heavy‐metal/ferromagnet can potentially be used to design low‐power spintronics and logic devices. Recent computations have suggested that a strain‐mediated spin–orbit torque (SOT) switching in magnetoelectric (ME) heterostructures is fast, energy‐efficient, and permits a deterministic 180° magnetization switching. However, its experimental realization has remained elusive. Here, the coexistence of the strain‐mediated ME coupling and the SOT in a CoFeB/Pt/ferroelectric hybrid structure is shown experimentally. The voltage‐induced strain only slightly modifies the efficiency of SOT generation, but it gives rise to an effective magnetic anisotropy and rotates the magnetic easy axis which eliminates the incubation delay in current‐induced magnetization switching. The phase field simulations show that the electric‐field‐induced effective magnetic anisotropy field can reduce the switching time approximately by a factor of three for SOT in‐plane magnetization switching. It is anticipated that such strain‐mediated ME‐SOT hybrid structures may enable field‐free, ultrafast magnetization switching.     

Comparison of CW THz Wave Spectrometer with Laser Diode Excitation and Pulsed THz Wave Spectrometer with Cr:forsterite Sources Based on Difference Frequency Generation of Near-infrared Lasers in GaP

We constructed two types of terahertz (THz) spectrometers with automatic scanning control based on the difference frequency generation method by the excitation of the phonon-polariton mode in GaP. The pulsed THz wave spectroscopic systems were based on an optical parametric oscillator and Nd: YAG laser sources having a frequency resolution of 1.5 GHz, and on Cr:fosterite sources with a resolution of 20 GHz. Following these, we recently constructed a continuous wave (CW) THz wave spectroscopic system with laser diode excitation. One of the advantages of the CW THz wave spectrometer is its wide frequency tuning range with fine frequency resolution of < 8 MHz. In this study, we compare both types of spectrometers (pulsed versus CW) to show the characteristics of each system in terms of frequency resolution. The absorption spectra of a non-deformed white polyethylene crystal and ultra-high molecular weight polyethylene with/without deformation are measured by using the CW THz wave spectrometer and pulsed THz wave spectrometer. The effect of the high-resolution CW THz wave spectrometer is shown based on the THz spectroscopic results.     

Terahertz Photon-Assisted Tunneling in InAs Quantum Dots

We have investigated electron transport in a single self-assembled InAs quantum dot (QD) coupled to nanogap metal electrodes under terahertz (THz) radiation. The fabricated QD samples operated as single electron transistors in a few electron regime, exhibiting clear shell structures. Under the THz radiation, in addition to the original Coulomb oscillation peaks, new side-peaks showed up. The dependence of the new side-peak current on the THz power follows the prediction of the photon-assisted tunneling (PAT) theory. Moreover, two types of PAT processes were observed in the THz range; the ground state resonance and the photon-induced excited state resonance, depending on the relative magnitude between the orbital quantization energy of the QDs and the THz photon energy. Furthermore, a very high coupling efficiency between the THz waves and the QDs was realized in our system and we observed multi-photon absorption up to the fourth-order during the tunneling process, resulting in almost complete lifting of the Coulomb blockade. This high coupling efficiency between THz wave and electrons in QDs opens a way to the manipulation of single electron charge/spin states in the THz frequency range.     

基于石墨烯的太赫兹光电功能器件研究进展

作为一种新型光电材料,石墨烯独特的能带结构和电子输运特性,使其与太赫兹科学有着密切的内在关系：石墨烯内部的等离子体振荡频率在太赫兹频段;人为调谐石墨烯的禁带宽度在0~0.3 eV时,正好覆盖太赫兹频段;光电导率的外部可控性等,这些特点使得石墨烯有望成为太赫兹频段新一代高性能设备研制的基础。最近的研究显示,石墨烯在太赫兹波产生、调控、检测等光电功能器件的研制中取得了很好的成果。重点介绍了基于石墨烯的太赫兹光电功能器件,包括太赫兹源器件、可控调控器件及检测器研究的最新进展,并对这一快速发展的研究领域进行了展望。