Abstract-Bifunctional terahertz absorber with a tunable and switchable property between broadband and dual-band

Hui Li and Jiang Yu

The electric field distribution of the proposed absorber at different perfect resonance frequencies (a-b) Top view; (c-d) Side view when the conductivity of VO2 is set to 200000S/m.

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-28-17-25225

In this paper, we propose a terahertz bifunctional absorber with broadband and dual-band absorbing properties based on a hybrid graphene-vanadium dioxide (VO2) metamaterial configuration. When VO2 is in the insulating state and the Fermi energy of graphene is set to 0.8 eV, the designed device behaves as a tunable perfect dual-band absorber. The operating bandwidth and magnitude of the dual-band spectrum can be continuously adjusted by changing the Fermi energy of graphene. When VO2 is changed from insulator to metal, the designed system can be regarded as a broadband absorber, it has a broad absorption band in the range of 1.45-4.37 THz, and the corresponding absorptance is more than 90%. The simulation results indicate that the absorptance can be dynamically changed from 17% to 99% by adjusting the conductivity of the VO2 when the Fermi energy of graphene is fixed at 0.01 eV. Besides, both dual absorption spectrum and broad absorption spectrum maintain a strong polarization-independent characteristic and operate well at wide incident angles. Furthermore, we have introduced the interference theory to explain the physical mechanism of the absorption from an optical method. Therefore, our designed system can be applied in many promising fields like cloaking and switch.

© 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Active KTaO3 hybrid terahertz metamaterial

• Liang Wu, 
• Jinglong Liu, 
• Hui Li, 
• Chunfeng Ding, 
• Ningning Xu, 
• Xiaolei Zhao, 
• Zongcheng Xu, 
• Quan Sheng, 
• Jianquan Yao, 
• Jining Li, 
• Xin Ding & 
• Weili Zhang

https://www.nature.com/articles/s41598-017-05529-0

The dielectric properties of an active KTaO3 hybrid metamaterial structure and its tunability under external electric fields are investigated at room temperature by means of terahertz time-domain spectroscopy. Application of the electric field leads to an appreciable tuning of the dielectric loss, which is up to 17%. Meanwhile, the refractive index also changes appreciably. These findings are attributed to the internal space charge field in the crystal caused by the excited free carriers.

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-Metamaterials: A New Ba0.6Sr0.4TiO3–Silicon Hybrid Metamaterial Device in Terahertz Regime

http://onlinelibrary.wiley.com/doi/10.1002/smll.201670098/full

A giant terahertz modulation based on a Ba0.6Sr0.4TiO3–silicon hybrid metamaterial is reported by L. Wu, W. Zhang, and co-workers on page 2610. The proposed nanoscale Ba0.6Sr0.4TiO3 (BST) hybrid metamaterial, delivering a transmission contrast of up to ≈79% due to electrically enabled carrier transport between the ferroelectric thin film and silicon substrate, is promising in developing high-performance real world photonic devices for terahertz technology.

Abstract-A New Ba0.6Sr0.4TiO3–Silicon Hybrid Metamaterial Device in Terahertz Regime

http://onlinelibrary.wiley.com/doi/10.1002/smll.201600276/full

Metamaterials, offering unprecedented functionalities to manipulate electromagnetic waves, have become a research hotspot in recent years. Through the incorporation of active media, the exotic electromagnetic behavior of metamaterials can be dramatically empowered by dynamic control. Many ferroelectric materials such as BaSrTiO3 (abbreviated as BST), exhibiting strong response to external electric field, hold great promise in both microwave and terahertz tunable devices. A new active Ba0.6Sr0.4TiO3–silicon hybrid metamaterial device, namely, a SRR (square split-ring resonator)–BaSrTiO3 thin film-silicon three-layer structure is fabricated and intensively studied. The active Ba0.6Sr0.4TiO3 thin film hybrid metamaterial, with nanoscale thickness, delivers a transmission contrast up to ≈79% due to electrically enabled carrier transport between the ferroelectric thin film and silicon substrate. This work has significantly increased the low modulation rate of ferroelectric based devices in terahertz range, a major problem in this field remaining unresolved for many years. The proposed BST metamaterial is promising in developing high-performance real world photonic devices for terahertz technology.