Abstract-Edge currents driven by terahertz radiation in graphene in quantum Hall regime

Helene Plank, M V Durnev, Susanne Candussio, Johanna Pernul, Kathrin-Maria Dantscher, Erwin Mönch, Andreas Sandner, Jonathan Eroms, Dieter Weiss, Vasily V Belkov

http://iopscience.iop.org/article/10.1088/2053-1583/aae39c

We observe that the illumination of  graphene in the quantum Hall regime with polarized terahertz laser radiation results in a direct edge current. This photocurrent is caused by an imbalance of persistent edge currents, which are driven out of thermal equilibrium by indirect transitions within the chiral edge channel. The direction of the edge photocurrent is determined by the polarity of the external magnetic field, while its magnitude depends on the radiation polarization. The microscopic theory developed in this paper describes well the experimental data.

Abstract-Terahertz electric field driven electric currents and ratchet effects in graphene

Sergey D. Ganichev, Dieter Weiss, Jonathan Eroms

(Submitted on 17 Oct 2017)

https://arxiv.org/abs/1710.06243#

Terahertz field induced photocurrents in graphene were studied experimentally and by microscopic modeling. Currents were generated by cw and pulsed laser radiation in large area as well as small-size exfoliated graphene samples. We review general symmetry considerations leading to photocurrents depending on linear and circular polarized radiation and then present a number of situations where photocurrents were detected. Starting with the photon drag effect under oblique incidence, we proceed to the photogalvanic effect enhancement in the reststrahlen band of SiC and edge-generated currents in graphene. Ratchet effects were considered for in-plane magnetic fields and a structure inversion asymmetry as well as ratchets by non-symmetric patterned top gates. Lastly, we demonstrate that graphene can be used as a fast, broadband detector of terahertz radiation.

Abstract-Terahertz split-ring metamaterials as transducers for chemical sensors based on conducting polymers: a feasibility study with sensing of acidic and basic gases using polyaniline chemosensitive layer

Christoph Drexler, 

Tatiana V. Shishkanova, 

Christoph Lange, 

Sergey N. Danilov, 

Dieter Weiss,

Sergey D. Ganichev, 

Vladimir M. Mirsky

http://link.springer.com/article/10.1007/s00604-014-1263-0
We report on the first application of terahertz metamaterials acting as transducers for chemical sensors based on conducting polymers. In our feasibility study aimed at sensing of gaseous hydrochloric and ammonia, a two-dimensional sensor metamaterial consisting of an array of split-ring resonators on the surface of undoped silicon wafer was prepared. The surface of the resonator was coated with a 150-μm layer of polyaniline. Binding of hydrogen chloride to polyaniline leads to distinct changes in the resonance frequency of the metamaterial. Measurements can be performed both in the reflection and transmission mode. A numerical simulation of the response revealed an increase of both the real and the imaginary components of the dielectric function of the polyaniline film. These changes are attributed to the transition from emaraldine base to emeraldine salt. The results demonstrate a new approach for formation of highly sensitive transducers for chemical sensors.