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Anisotropic spin transport and photoresponse characteristics detected by tip movement in magnetic single-molecule junction

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Chinese Physics B 2024年第4期33卷 640-648页

作者：陈登辉羊志付新宇秦申奥严岩王传奎李宗良邱帅 Shandong Key Laboratory of Medical Physics and Image Processing&Shandong Provincial Engineering and Technical Center of Light Manipulations School of Physics and ElectronicsShandong Normal UniversityJinan 250358China

Orientation-dependent transport properties induced by anisotropic molecules are enticing in single-molecule junctions.Here,using the first-principles method,we theoretically investigate spin transport properties and photoresponse characteristics in trimesic acid magnetic single-molecule junctions with different molecular adsorption orientations and electrode contact sites.The transport calculations indicate that a single-molecule switch and a significant enhancement of spin transport and photoresponse can be achieved when the molecular adsorption orientation changes from planar geometry to upright geometry.The maximum spin polarization of current and photocurrent in upright molecular junctions exceeds 90%.Moreover,as the Ni tip electrode moves,the tunneling magnetoresistance of upright molecular junctions can be increased to 70%.The analysis of the spin-dependent PDOS elucidates that the spinterfaces between organic molecule and ferromagnetic electrodes are modulated by molecular adsorption orientation,where the molecule in upright molecular junctions yields higher spin polarization.Our theoretical work paves the way for designing spintronic devices and optoelectronic devices with anisotropic functionality base on anisotropic molecules.

关键词： molecular spintronics spin polarization tunneling magnetoresistance photocurrent single-molecule junctions

Cornerstone of molecular spintronics: Strategies for reliable organic spin valves

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Nano Research 2021年第11期14卷 3653-3668页

作者： Shuaishuai Ding Yuan Tian Wenping Hu Tianjin Key Laboratory of molecular Optoelectronic Sciences Department of ChemistrySchool of SciencesTianjin UniversityTianjin300072China School of Physics&Electronics Hunan UniversityHunan410082China Collaborative Innovation Center of Chemical Science and Engineering Tianjin300072China Joint School of National University of Singapore and Tianjin University International Campus of Tianjin UniversityBinhai New CityFuzhou350207China

Organic spin valve (OSV), one of the most promising and representative devices involving spin injection, transport and detection, has drawn tremendous attention owing to their ultra-long spin relaxation time in the field of molecular spintronics. Since the first demonstration of truly worked vertical OSV device in 2004, efforts in enhancement of high performance and pursuit of spin-related nature have been devoted in related field. It offers a new opportunity to develop the integrated flexible multi-functional arrays based on spintronics in the future. However, the unreliable working state in OSVs due to the lack of exploration on interface control will cause severe impact on the performance evaluation and further restrict their practical application. Herein, we focus on the recent progress in strategies for reliable fabrication and evaluation of typical OSVs in vertical configuration. Firstly, the challenges in protection of two spin interface properties and identification of spin-valve-like signals were proposed. Then, three points for attention including selection of bottom electrodes, optimization of organic spacer, and prevention of metal penetration to improve the device performance and reliability were mentioned. Particularly, various modified strategies to solve the “dead layer” issue were highlighted. Furthermore, we discussed the general protocols in the reliable evaluation of OSVs’ performance and transport mechanism identification. Notably, several key fundamentals resulting in spurious magnetoresistance (MR) response were illustrated. Finally, we also highlighted the future perspectives on spintronic devices of organic materials.

关键词： molecular spintronics organic spin valves magnetoresistance device reliability fair performance evaluation

molecular design for enhanced spin transport in molecular semiconductors

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Nano Research 2023年第12期16卷 13457-13473页

作者： Tingting Yang Yang Qin Xianrong Gu Xiangnan Sun Key Laboratory of Nanosystem and Hierarchical Fabrication CAS Center for Excellence in NanoscienceNational Center for Nanoscience and TechnologyBeijing 100190China Center of Materials Science and Optoelectronics Engineering University of Chinese Academy of SciencesBeijing 100049China School of Material Science and Engineering Zhengzhou UniversityZhengzhou 450001China

molecular semiconductors(MSCs),characterized by a longer spin lifetime than most of other materials due to their weak spin relaxation mechanisms,especially at room temperature,together with their abundant chemical tailorability and flexibility,are regarded as promising candidates for spintronic applications.molecular spintronics,as an emerging subject that utilizes the unique properties of MSCs to study spin-dependent phenomena and properties,has attracted wide attention.In molecular spintronic devices,MSCs play the role as medium for information transport,process,and storage,in which the efficient spin inject–transport process is the prerequisite.Herein,we focus mainly on summarizing and discussing the recent advances in theoretical principles towards spin transport of MSCs in terms of the injection of spin-polarized carriers through the ferromagnetic metal/MSC interface and the subsequent transport within the MSC layer.Based on the theoretical progress,we cautiously present targeted design strategies of MSCs that contribute to the optimization of spin-transport efficiency and give favorable approaches to exploring accessional possibilities of spintronic materials.Finally,challenges and prospects regarding current spin transport are also presented,aiming to promote the development and application of the rosy and energetic field of molecular spintronics.

关键词： molecular spintronics molecular semiconductors spin transport spin injection molecular design

Room-Temperature Single-Molecule Conductance Switch via Confined Coordination-Induced Spin-State Manipulation

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CCS Chemistry 2022年第4期4卷 1357-1365页

作者： Jing Li Qingqing Wu Wei Xu Hai-Chuan Wang Hewei Zhang Yaorong Chen Yongxiang Tang Songjun Hou Colin JLambert Wenjing Hong State Key Laboratory of Physical Chemistry of Solid Surfaces College of Chemistry and Chemical EngineeringXiamen UniversityXiamen 361005 Department of Physics Lancaster UniversityLancaster LA14YB

The emergence of molecular spintronics offers a unique chance for the design of molecular devices with different spin-states,and the control of spin-state becomes essential for molecular spin switches.However,the intrinsic spin switching from low-to high-spin state is a temperature-dependent process with a small energy barrier where low temperature is required to maintain the low-spin state.Thus,the room-temperature operation of single-molecule devices has not yet been achieved.Herein,we present a reversible single-molecule conductance switch by manipulating the spin states of the molecule at room temperature using the scanning tunneling microscope break-junction(STM-BJ)technique.The manipulation of the spin states between S=0 and S=1 is achieved by complexing or decomplexing the pyridine derivative molecule with a square planar nickel(Ⅱ)porphyrin.The bias-dependent conductance evolution proves that the strong electric field between the nanoelectrodes plays a crucial role in the coordination reaction.The density functional theory(DFT)calculations further reveal that the conductance changes come from the geometric changes of the porphyrin ring and spin-state switching of the Ni(Ⅱ)ion.Our work provides a new avenue to investigate room-temperature spin-related sensors and molecular spintronics.

关键词： confined coordination-induced spinstate manipulation molecular spintronics nickel(Ⅱ)porphyrin break junctions

Current spin polarization of a platform molecule with compression effect

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Chinese Physics B 2022年第7期31卷 498-504页

作者：羊志孙峰陈登辉王子群王传奎李宗良邱帅 Shandong Key Laboratory of Medical Physics and Image Processing&Shandong Provincial Engineering and Technical Center of Light Manipulations School of Physics and ElectronicsShandong Normal UniversityJinan 250358China Zao Zhuang University Zao Zhuang 277160China

Using the first-principles method,the spin-dependent transport properties of a novel platform molecule containing a freestanding molecular wire is investigated by simulating the spin-polarized scanning tunneling microscope experiment with Ni tip and Au substrate electrodes.Transport calculations show that the total current increases as the tip gradually approaches to the substrate,which is consistent with the conductance obtained from previous experiment.More interestingly,the spin polarization(SP)of current modulated by compression effect has the completely opposite trend to the total current.Transmission analyses reveal that the reduction of SP of current with compression process originates from the promotion of spin-down electron channel,which is controlled by deforming the molecule wire.In addition,the density of states shows that the SP of current is directly affected by the organic–ferromagnetic spinterface.The weak orbital hybridization between the Ni tip and propynyl of molecule results in high interfacial SP,whereas the breaking of the C≡C triple of propynyl in favor of the Ni–C–C bond induces the strong orbital hybridization and restrains the interfacial SP.This work proposes a new way to control and design the SP of current through organic–ferromagnetic spinterface using functional molecular platform.

关键词： molecular spintronics spin-dependent transport spin polarization single-molecule junctions

Kondo effect in a deformed molecule coupled asymmetrically to ferromagnetic electrodes

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Chinese Physics B 2009年第12期18卷 5443-5450页

作者：王瑞强蒋开明 Laboratory of Quantum Information Technology Institute for Condensed Matter Physicsand School of Physics and Telecommunication EngineeringSouth China Normal University Department of Physics Shanghai Maritime University

The nonequilibrium Kondo effect is studied in a molecule quantum dot coupled asymmetrically to two ferromagnetic electrodes by employing the nonequilibrium Green function technique. The current-induced deformation of the molecule is taken into account, modeled as interactions with a phonon system, and phonon-assisted Kondo satellites arise on both sides of the usual main Kondo peak. In the antiparallel electrode configuration, the Kondo satellites can be split only for the asymmetric dot-lead couplings, distinguished from the parallel configuration where splitting also exists, even though it is for symmetric case. We also analyze how to compensate the splitting and restore the suppressed zero-bias Kondo resonance. It is shown that one can change the TMR ratio significantly from a negative dip to a positive peak only by slightly modulating a local external magnetic field, whose value is greatly dependent on the electron-phonon coupling strength.

关键词： Kondo effect molecular spintronics tunneling magnetoresistance electron phonon interaction nonequilibrium Green function

Recent spinterfacial studies targeted to spin manipulation in molecular spintronic devices

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Chinese Physics B 2018年第10期27卷 96-106页

作者：谷现荣郭立丹孙向南 CAS Key Laboratory of Nanosystem and Hierarchical Fabrication CAS Center for Excellence in Nanoscience National Center for Nanoscience and Technology Beijing 100190 China University of Chinese Academy of Sciences (CAS) Beijing 100049 China Department of Materials Science and Engineering College of New Energy and Materials China University of Petroleum Beijing Beijing 102249 China

molecular spintronics is an emerging field which evoked wide research attention since the first molecule-based spintronic device has been reported at 2002. Due to the active study over the last few years, it is found that the interfaces in spintronic device, so called spinterface, is of critical importance for many key issues in molecular spintronics, such as enhancing spin injection, lengthening spin transport distance, as well as manipulating spin signals in molecular spintronic devices. Here in this review, recent studies regarding spinterface in molecular devices, especially those impressive efforts devoted on spin manipulation, have been systematically summarized and discussed.

关键词： molecular spintronics spin valve spinterface spin manipulation