Abstract-Terahertz Spin Transfer Torque Oscillator Based on a Synthetic Antiferromagnet

Hai Zhong, Shizhu Qiao, Shishen Yan, Hong Zhang, Yufeng Qin, Lanju Liang, Dequan Wei, Yinrui Zhao, Shishou Kang

https://arxiv.org/abs/1807.11633

Bloch-Bloembergen-Slonczewski equation is adopted to simulate magnetization dynamics in spin-valve based spin-transfer torque oscillator with synthetic antiferromagnet acting as a free magnetic layer. High frequency up to the terahertz scale is predicted in synthetic antiferromagnet spin-transfer torque oscillator with no external magnetic field if the following requirements are fulfilled: antiferromagnetic coupling between synthetic antiferromagnetic layers is sufficiently strong, and the thickness of top (bottom) layer of synthetic antiferromagnet is sufficiently thick (thin) to achieve a wide current density window for the high oscillation frequency. Additionally, the transverse relaxation time of the free magnetic layer should be sufficiently larger compared with the longitudinal relaxation time. Otherwise, stable oscillation cannot be sustained or scenarios similar to regular spin valve-based spin-transfer torque oscillator with relatively low frequency will occur. Our calculations pave a new way for exploring THz spintronics devices.

Abstract-Tunable Localized Surface Plasmon Resonances in a New Graphene-Like Si2BN’s Nanostructures

• Shi-Jia Yuan, 
• Hong Zhang, 
Xin-Lu Cheng

https://link.springer.com/article/10.1007/s11468-017-0592-3

The optical response of a new graphene-like material Si2BN’s nanostructures and some kinds of hybrid structures formed by Si2BN and metal nanoparticles was studied by using time-dependent density functional theory (TDDFT). We found that the periodic structures of Si2BN have wider absorption ranges than graphene. When the impulse excitation polarizes in different directions (armchair-edge direction and zigzag-edge direction), the absorption spectra of Si2BN nanostructures would be different (optical anisotropy). And in the hybrid structures, the increase of metal nanoparticles’ number brings the absorption intensity strengthening and red shift, which means a stronger ability of localized surface plasmon tuning. Also, the different metal nanoparticles were used to form the hybrid structures; they show an obviously different property as well. In addition, in the kinds of situations mentioned above, the plasmons were produced in visible region. This investigation provides an improved understanding of the plasmon enhancement effect in graphene-like photoelectric devices.

Abstract-The effect of temperature, defect and strain rate on the mechanical property of multi-layer graphene: coarse-grained molecular dynamics study

Hui Li^a,Hong Zhang^{b, c,} ,Xinlu Cheng^{a, c}

• ^a Institute of Atomic and Molecular Physics, Sichuan University, Chengdu 610065, China
• ^b College of Physical Science and Technology, Sichuan University, China, Chengdu 610065,China
• ^c Key Laboratory of High Energy Density Physics and Technology of Ministry of Education, Sichuan University, Chengdu, 610064, China

http://www.sciencedirect.com/science/article/pii/S1386947716305173

In this work, we investigate the effect of temperature, defect, and strain rate on the mechanical properties of multi-layer graphene using coarse-grained molecular dynamics (CGMD) simulations. The simulation results reveal that the mechanical properties of multi-layer graphene tend to be less sensitive to temperature as the layer increases, but they are sensitive to the distribution and coverage of Stone-Wales (SW) defects. For the same number of defect, there is less decline in the fracture stress and Young's modulus of graphene when the defects have a regular distribution, in contrast to random distribution. In addition, Young's modulus is less influenced by temperature and defect, compared to fracture stress. Both the fracture stress and Young's modulus have little dependence on strain rate.

Abstract-Optical field terahertz amplitude modulation by graphene nanoribbons

Hong Zhang,*^a   Yoshiyuki Miyamoto,^b   Xinlu Cheng^c and  Angel Rubio^def  

http://pubs.rsc.org/en/content/articlelanding/2015/nr/c5nr05889a#!divAbstract

*

Corresponding authors

^a

College of Physical Science and Technology, Sichuan University, Chengdu 610065, China
E-mail: hongzhang@scu.edu.cn

^b

Nanomaterials Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Central 2, 1-1-1 Umezono, Tsukuba 305-8568, Japan

^c

Key Laboratory of High Energy Density Physics and Technology of Ministry of Education; Sichuan University, Chengdu, China

^d

Max Planck Institute for the Structure and Dynamics of Matter, Hamburg, Germany

^e

Nano-Bio Spectroscopy group, Universidad del País Vasco CFM CSIC-UPV/EHU-MPC DIPC, 20018 San Sebastian, Spain

^f

European Theoretical Spectroscopy Facility (ETSF)

Nanoscale, 2015, Advance Article

DOI: 10.1039/C5NR05889A






















In this study, first-principles time-dependent density functional theory calculations were used to demonstrate the possibility to modulate the amplitude of the optical electric field (E-field) near a semiconducting graphene nanoribbon. A significant enhancement of the optical E-field was observed 3.34 Å above the graphene nanoribbon sheet, with an amplitude modulation of approximately 100 fs, which corresponds to a frequency of 10 THz. In general, a six-fold E-field enhancement could be obtained, which means that the power of the obtained THz is about 36 times that of incident UV light. We suggest the use of semiconducting graphene nanoribbons for converting visible and UV light into a THz signal.