Abstract-Separation of valley excitons in a MoS2 monolayer using a subwavelength asymmetric groove array

Liuyang Sun, Chun-Yuan Wang, Alex Krasnok, Junho Choi, Jinwei Shi, Juan Sebastian Gomez-Diaz, André Zepeda, Shangjr Gwo, Chih-Kang Shih, Andrea Alù, Xiaoqin Li

https://www.nature.com/articles/s41566-019-0348-z

Excitons in monolayer transition metal dichalcogenides are formed at K and K′ points at the boundary of the Brillouin zone. They acquire a valley degree of freedom, which has been explored as an alternative information carrier, analogous to charge or spin. Two opposite valleys in transition metal dichalcogenides can be optically addressed using light with different helicity. Here, we demonstrate that valley-polarized excitons can be sorted and spatially separated at room temperature by coupling a MoS2 monolayer to a subwavelength asymmetric groove array. In addition to separation of valley excitons in real space, emission from valley excitons is also separated in photon momentum-space; that is, the helicity of photons determines a preferential emission direction. Our work demonstrates that metasurfaces can facilitate valley transport and establish an interface between valleytronic and photonic devices, thus addressing outstanding challenges in the field of valleytronics.

Abstract -Nanostructured graphene metasurface for tunable terahertz cloaking

Pai-Yen Chen1, Jason Soric1, Yashwanth R Padooru2, Hossein M Bernety2, Alexander B Yakovlev2 and Andrea Alù1,3

http://iopscience.iop.org/1367-2630/15/12/123029/article;jsessionid=CFFC252A066AB15BD39AA849D2CEA0DF.c1

alu@mail.utexas.edu

1 Department of Electrical and Computer Engineering, University of Texas at Austin, Austin, TX 78712, USA
2 Center for Applied Electromagnetic Systems Research (CAESR), Department of Electrical Engineering, The University of Mississippi, University, MS 38677-1848, USA
3 Author to whom any correspondence should be addressed. 

Pai-Yen Chen et al 2013 New J. Phys. 15 123029
doi:10.1088/1367-2630/15/12/123029
© IOP Publishing and Deutsche Physikalische Gesellschaft
Received 20 July 2013
Published 17 December 2013

We propose and analyze a graphene-based cloaking metasurface aimed at achieving widely tunable scattering cancelation in the terahertz (THz) spectrum. This 'one-atom-thick' mantle cloak is realized by means of a patterned metasurface comprised of a periodic array of graphene patches, whose surface impedance can be modeled with a simple yet accurate analytical expression. By adjusting the geometry and Fermi energy of graphene nanopatches, the metasurface reactance may be tuned from inductive to capacitive, as a function of the relative kinetic inductance and the geometric patch capacitance, enabling the possibility of effectively cloaking both dielectric and conducting objects at THz frequencies with the same metasurface. We envision applications for low-observable nanostructures and efficient THz sensing, routing and detection.

Paper-A terahertz photomixer based on plasmonic nanoantennas coupled to a graphene emitter

Pai-Yen Chen¹ and Andrea Alù
http://iopscience.iop.org/0957-4484/24/45/455202;jsessionid=662617F0AD91E1046CDC2A989905027D.c2

pychen@utexas.edu alu@mail.utexas.edu
Department of Electrical and Computer Engineering, The University of Texas at Austin, 1 University Station C0803, Austin, TX 78712, USA

We propose the concept of a graphene-based nanoantenna-enhanced photomixer to realize wideband-tunable terahertz (THz) frequency generation. When two laser beams are focused on the graphene nanoemitter of a planar field-emission diode, THz current oscillations can be created at the emitter tip through the optical heterodyne. Graphene's optical transparency allows suitably designed plasmonic nanoantennas to boost the mixing of laser radiation at the emitter tip, significantly increasing the overall produced photomixing current. The THz wave generated at the graphene emitter is then coupled to a loading circuit, thanks to the THz wave confinement in the graphene nanostructures. Our design is ideally suited for THz sources that may be tuned from DC to 10 THz by simply shifting the frequency offset of two pumping lasers.

Abstract-Broadband absorbers and selective emitters based on plasmonic Brewster metasurfaces

Christos Argyropoulos, Khai Q. Le, Nadia Mattiucci, Giuseppe D’Aguanno, and Andrea Alù
http://prb.aps.org/accepted/05070Yf8Lc61cb36442323938b3318674ea3f2929

We discuss the possibility of realizing utlrabroadband omnidirectional absorbers and angularly selective coherent thermal emitters based on properly patterned plasmonic metastructures. Instead of relying on resonant concentration effects that inherently limit the bandwidth, we base our design on the combination of two inherently nonresonant effects: plasmonic Brewster funneling and adiabatic plasmonic focusing. Using this approach, we propose compact, broadband absorption and emission spanning terahertz, infrared and optical frequencies, ideal for various energy and defense applications.

Texas Now Has The Thinnest Invisibility Cloak

Image via Wikipedia

http://www.crazyengineers.com/texas-now-has-the-thinnest-invisibility-cloak-535/

Cloaking devices i.e.; the invisibility cloaks are recently a topic of key focus for scientists. With recent developments like the ‘inaudibility cloaks’ and the previous ‘invisibility cloaks’, man’s hiding capabilities have been greatly increased. Though both the cloaks are yet to be commercialized, still we may say that we have got some basic concepts correct and most importantly we now have the Aladdin’s lamp or simply the metamaterials.

Researchers from University of Texas, Austin have developed a thinnest possible invisibility cloak till date. A research team led by prof. Andrea Alù, Dept. of Electrical and Computer engineering has put forward a concept of Mantle cloaking which revolves around using simple impedance surface to have an invisibility effect. Scientists have used Graphene as a material for making this cloak. Alù and his team members have proposed a material which can be tuned to a microwave frequency for which the material can adjust its surface impedance.

Development path for the recent invisibility cloak

Graphene is a promising material in today’s research area. Scientists from all over the world are trying to study as to how Graphene responds when subjected to AC. They are also trying to notice changes, if any, in conductivity of the material subjected to AC. In context of these researches, University of Texas team have observed that Graphene has the required surface impedance owing to its properties like easily tuned Fermi level and its ultra high mobility. So, the cloak can be tuned at will which also means that you can switch the cloak as per your need. The concept can also be applied in the Terahertz spectrum and leads to a thinnest possible cloak till date.

The concept and more importantly the ‘tunable’ properties of Graphene, will be well utilized in development of numerous other applications like non invasive sensors, low scattering electronic sensors and other IR switching devices which can be incorporated in monolithic photonic circuitry. The group had also presented a concept earlier in 2005 about Plasmonic cloaking. This idea is based on preventing the scattering from any passive object.

According to Alù, “The field of metamaterials, plasmonics and advanced materials, on which we are active since several years, holds the promise of revolutionizing current technology”. It seems he is correct in saying that because, there are still greater chances of compatibility of current technology with existing electronic components making them really advanced and upgrade them to changing times.

Source: Nanowerk