Abstract-Terahertz frequency spectrum analysis with a nanoscale antiferromagnetic tunnel junction

Journal of Applied Physics

Sulymenko,  S. Louis, J. Li,  R. S. Khymyn, E. Bankowski,  T. Meitzler,  V. S. Tyberkevych,  A. N. Slavin,  O. V. Prokopenko,

(a) Pt/AFM/MgO/Pt antiferromagnetic tunnel junction (ATJ). The driving dc current Idrive(t)$I_{\mathrm{drive}}(t)$ flowing in the bottom Pt layer of an ATJ generates the transverse spin current ISH$I_{\mathrm{SH}}$ flowing into the AFM layer, which excites the TF rotation of magnetization of the AFM sublattices and, consequently, the TF variations of the junction resistance R(t)$R(t)$. When a TF signal with power Ps$P_s$ and frequency fs$f_s$ is supplied to the junction, its action results in the generation of voltage Uatj$U_{\mathrm{atj}}$ across the whole structure. (b) A simplified equivalent electric scheme of the ATJ-based detector connected through an ideal bias tee to a source of an external TF signal.

https://aip.scitation.org/doi/10.1063/1.5140552

A method to perform spectrum analysis on low power signals between 0.1$0.1$ and 10 THz is proposed. It utilizes a nanoscale antiferromagnetic tunnel junction (ATJ) that produces an oscillating tunneling anisotropic magnetoresistance, whose frequency is dependent on the magnitude of an evanescent spin current. It is first shown that the ATJ oscillation frequency can be tuned linearly with time. Then, it is shown that the ATJ output is highly dependent on matching conditions that are highly dependent on the dimensions of the dielectric tunneling barrier. Spectrum analysis can be performed by using an appropriately designed ATJ, whose frequency is driven to increase linearly with time, a low pass filter, and a matched filter. This method of THz spectrum analysis, if realized in the experiment, will allow miniaturized electronics to rapidly analyze low power signals with a simple algorithm. It is also found by simulation and analytical theories that for an ATJ with a 0.09μm2$0.09\mu {\mathrm{m}}^2$ footprint, spectrum analysis can be performed over a 0.25THz$0.25\mathrm{THz}$ bandwidth in just 25 ns on signals that are at the Johnson–Nyquist thermal noise floor.

Abstract-A high-performance broadband terahertz absorber based on sawtooth-shape doped-silicon

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Liang-Hui Du1,2,a), Jiang Li1,2, Zhao-Hui Zhai1,2, Kun Meng1,2, Qiao Liu1,2, Sen-Cheng Zhong1,2, Ping-Wei Zhou1,2, Li-Guo Zhu1,2,b), Ze-Ren Li1,2 and Qi-Xian Peng1,2

a) Electronic mail: Lianghui_Du@163.com

b) Electronic mail: zhuliguo@tsinghua.org.cn

AIP Advances 6, 055112 (2016); http://dx.doi.org/10.1063/1.4950800

http://scitation.aip.org/content/aip/journal/adva/6/5/10.1063/1.4950800?TRACK=RSS

Perfect absorbers with broadband absorption of terahertz (THz) radiation are promising for applications in imaging and detection to enhance the contrast and sensitivity, as well as to provide concealment. Different from previous two-dimensional structures, here we put forward a new type of THz absorber based on sawtooth-shape doped-silicon with near-unit absorption across a broad spectral range. Absorbance over 99% is observed numerically from 1.2 to 3 THz by optimizing the geometric parameters of the sawtooth structure. Our absorbers can operate over a wide range of incident angle and arepolarization insensitive. The underlying mechanisms due to the combination of an air-cavity mode and mode-matching resonance on the air-sawtooth interface are analyzed in terms of the field patterns and electromagnetic power loss features.

Abstract-Graphene based plasmonic terahertz amplitude modulator operating above 100 MHz

D. S. Jessop1,a), S. J. Kindness1, L. Xiao2, P. Braeuninger-Weimer2, H. Lin3,b), Y. Ren1, C. X. Ren4, S. Hofmann2, J. A. Zeitler3, H. E. Beere1, D. A. Ritchie1 and R. Degl'Innocenti1,a)

a) Authors to whom correspondence should be addressed. Electronic addresses:dsj23@cam.ac.uk and rd448@cam.ac.uk.

b) Now at Department of Engineering, Lancaster University, Lancaster LA1 4YW, United Kingdom.

Appl. Phys. Lett. 108, 171101 (2016); http://dx.doi.org/10.1063/1.4947596

The terahertz (THz) region of the electromagnetic spectrum holds great potential in many fields of study, from spectroscopy to biomedical imaging, remote gas sensing, and high speed communication. To fully exploit this potential, fast optoelectronic devices such as amplitude and phase modulators must be developed. In this work, we present a room temperature external THz amplitude modulator based on plasmonic bow-tie antenna arrays with graphene. By applying a modulating bias to a back gate electrode, the conductivity of graphene is changed, which modifies the reflection characteristics of the incoming THz radiation. The broadband response of the device was characterized by using THz time-domain spectroscopy, and the modulation characteristics such as the modulation depth and cut-off frequency were investigated with a 2.0 THz single frequency emission quantum cascade laser. An optical modulation cut-off frequency of 105 ± 15 MHz is reported. The results agree well with a lumped element circuit model developed to describe the device.

Abstract-Enhanced microwave-to-terahertz absorption in graphene

K. Batrakov1,a), P. Kuzhir1, S. Maksimenko1, N. Volynets1, S. Voronovich1, A. Paddubskaya2, G. Valusis2, T. Kaplas3, Yu. Svirko3 andPh. Lambin4
 HIDE AFFILIATIONS
1 Research Institute for Nuclear Problems, Belarusian State University, Minsk 220030, Belarus
2 Center for Physical Sciences and Technology, A. Gostauto 11, Vilnius LT-01108, Lithuania
3 Institute of Photonics, University of Eastern Finland, Joensuu FI-80101, Finland
4 Physics Department, Universite de Namur, 61 Rue de Bruxelles, B-5000 Namur, Belgium
a) Electronic mail: kgbatrakov@gmail.com.
Appl. Phys. Lett. 108, 123101 (2016); http://dx.doi.org/10.1063/1.4944531

Fresnel equations predict that an ultrathin free standing conductive film, thousands times thinner than skin depth, is capable to absorb up to 50% of incident electromagnetic radiations. In the microwave range, the same holds true for a free standing graphene sheet. We demonstrate theoretically and prove experimentally that microwave absorptance of graphene can be enhanced considerably by depositinggraphene on a dielectric substrate. On the experimental side, we obtain 80% and 65% absorptance at 30 GHz and 1 THz, respectively. Theory predicts that higher absorptance can be achieved with a suitable choice of the dielectricpermittivity and the thickness of the substrate. Absorption can also be maximized by choosing the optimum incidence angle for s-polarized waves in free space or by working in the vicinity of the cut-off frequency of the transverse electric mode in waveguide configuration. The polarizationsensitivity of the transmittance and reflectance of graphene layers can be used to tune the polarizationstate of the transmitted and reflected radiations.

Abstract-Giant nonlinearity in a superconducting sub-terahertz metamaterial

V. Savinov1,a), K. Delfanazari1, V. A. Fedotov1 and N. I. Zheludev1,2

1 Optoelectronics Research Centre and Centre for Photonic Metamaterials, University of Southampton, Southampton, SO17 1BJ, United Kingdom

2 Centre for Disruptive Photonic Technologies, TPI, Nanyang Technological University, Singapore 637371, Singapore

a) vs1106@orc.soton.ac.uk

Appl. Phys. Lett. 108, 101107 (2016);

 http://dx.doi.org/10.1063/1.4943649

We report a superconducting sub-THz metamaterial operating in a CW-regime, which exhibits a record-breaking resonant third-order nonlinearity with effective n2∼10 cm2/W$n_2\sim 10\hspace{0.17em}{\text{cm}}^2/\mathrm{W}$. The nonlinear response is caused by the radiation-induced resistive heating, suppressing the superconductivity in the nano-scale constrictions of the structure's meta-molecules. The nonlinearity has a relaxation time of 25 μs$25\hspace{0.17em}\mu \mathrm{s}$ and leads to a substantial change of the amplitude and phase of the transmitted radiation at intensities of only 500 μW/cm2$500\hspace{0.17em}\mu {\mathrm{W}/\text{cm}}^2$.