Abstract-On-chip terahertz modulation and emission with integrated graphene junctions

Joshua O. Island, Peter Kissin, Jacob Schalch, Xiaomeng Cui, Sheikh Rubaiat Ul Haque, Alex Potts, Takashi Taniguchi, Kenji Watanabe, Richard D. Averitt, Andrea F. Young

https://arxiv.org/abs/2004.02059

The efficient modulation and control of ultrafast signals on-chip is of central importance in terahertz (THz) communications and a promising route toward sub-diffraction limit THz spectroscopy. Two-dimensional (2D) materials may provide a platform for these endeavors. We explore this potential, integrating high-quality graphene p-n junctions within two types of planar transmission line circuits to modulate and emit picosecond pulses. In a coplanar stripline geometry, we demonstrate electrical modulation of THz signal transmission by 95%. In a Goubau waveguide geometry, we achieve complete gate-tunable control over THz emission from a photoexcited graphene junction. These studies inform the development of on-chip signal manipulation and highlight prospects for 2D materials in THz applications.

Abstract-Ultrafast terahertz spectroscopy study of a Kondo insulating thin-film SmB 6 : Evidence for an emergent surface state

Jingdi Zhang, Jie Yong, Ichiro Takeuchi, Richard L. Greene, and Richard D. Averitt

https://journals.aps.org/prb/accepted/6b07fYbfWfc1334e19c50870d090a278ce468c67d

We utilize terahertz time domain spectroscopy to investigate thin films of the heavy fermion compound SmB6, a prototype Kondo insulator. Temperature dependent terahertz (THz) conductivity measurements reveal a rapid decrease in the Drude weight and carrier scattering rate at ~T*=20 K, well below the hybridization gap onset temperature (100 K). Moreover, a low-temperature conductivity plateau (below 20K) indicates the emergence of a surface state with an effective electron mass of 0.1me. Conductivity dynamics following optical excitation are also measured and interpreted using Rothwarf-Taylor (R-T) phenomenology, yielding a hybridization gap energy of 17 meV. However, R-T modeling of the conductivity dynamics reveals a deviation from the expected thermally excited quasiparticle density at temperatures below 20K, indicative of another channel opening up in the low energy electrodynamics. Taken together, these results suggest the onset of a surface state well below the crossover temperature (100K) after long-range coherence of the f-electron Kondo lattice is established.

Abstract-Electromechanically tunable metasurface transmission waveplate at terahertz frequencies

Xiaoguang Zhao, Jacob Schalch, Jingdi Zhang, Huseyin R. Seren, Guangwu Duan, Richard D. Averitt, and Xin Zhang

https://www.osapublishing.org/optica/abstract.cfm?uri=optica-5-3-303

Dynamic polarization control of light is essential for numerous applications ranging from enhanced imaging to material characterization and identification. We present a reconfigurable terahertz metasurface quarter-wave plate consisting of electromechanically actuated microcantilever arrays. Our anisotropic metasurface enables tunable polarization conversion through cantilever actuation. Specifically, voltage-based actuation provides mode-selective control of the resonance frequency, enabling real-time tuning of the polarization state of the transmitted light. The polarization tunable metasurface has been fabricated using surface micromachining and characterized using terahertz time domain spectroscopy. We observe a ∼230  GHz$\sim 230\mathrm{GHz}$ cantilever actuated frequency shift of the resonance mode, sufficient to modulate the transmitted wave from pure circular polarization to linear polarization. Our CMOS-compatible tunable quarter-wave plate enriches the library of terahertz optical components, thereby facilitating practical applications of terahertz technologies.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Structural Control of Metamaterial Oscillator Strength and Electric Field Enhancement at Terahertz Frequencies

George R. Keiser, Huseyin R. Seren, Andrew C. Strikwerda, Xin Zhang, Richard D. Averitt

(Submitted on 4 Jun 2014)

The design of artificial nonlinear materials requires control over the internal resonant charge densities and local electric field distributions. We present a MM design with a structurally controllable oscillator strength and local electric field enhancement at terahertz frequencies. The MM consists of a split ring resonator (SRR) array stacked above an array of nonresonant closed conducting rings. An in-plane, lateral shift of a half unit cell between the SRR and closed ring arrays results in a decrease of the MM oscillator strength by a factor of 4 and a 40% change in the amplitude of the resonant electric field enhancement in the SRR capacitive gap. We use terahertz time-domain spectroscopy and numerical simulations to confirm our results and we propose a qualitative inductive coupling model to explain the observed electromagnetic reponse.