Abstract-Manifestation of kinetic-inductance in spectrally-narrow terahertz plasmon resonances in thin-film Cd3As2

Ashish Chanana, Neda Loftizadeh, Hugo O. Condori Quispe, Prashanth Gopalan, Joshua R. Winger, Steve Blair, Ajay Nahata, Vikram Deshpande, Michael A. Scarpulla, Berardi Sensale-Rodriquez,

https://arxiv.org/abs/1811.04306

Three-dimensional (3D) semimetals have been predicted and demonstrated to have a wide variety of interesting properties associated with its linear energy dispersion. In analogy to two-dimensional (2D) Dirac semimetals, such as graphene, Cd3As2, a 3D semimetal, has shown ultra-high mobility, large Fermi velocity, and has been hypothesized to support plasmons at terahertz frequencies. In this work, we demonstrate synthesis of high-quality large-area Cd3As2 thin-films through thermal evaporation as well as the experimental realization of plasmonic structures consisting of periodic arrays of Cd3As2 stripes. These arrays exhibit sharp resonances at terahertz frequencies with associated quality-factors (Q) as high as ~ 3.7. Such spectrally-narrow resonances can be understood on the basis of a large kinetic-inductance, resulting from a long momentum scattering time, which in our films can approach ~1 ps at room-temperature. Moreover, we demonstrate an ultrafast tunable response through excitation of photo-induced carriers in optical pump / terahertz probe experiments. Our results evidence that the intrinsic 3D nature of Cd3As2 provides for a very robust platform for terahertz plasmonic applications. Overall, our observations pave a way for the development of myriad terahertz (opto) electronic devices based on Cd3As2 and other 3D Dirac semimetals, benefiting from strong coupling of terahertz radiation, ultrafast transient response, magneto-plasmon properties, etc. Moreover, the long momentum scattering time, thus large kinetic inductance in Cd3As2, also holds enormous potential for the re-design of passive elements such as inductors and hence can have a profound impact in the field of RF integrated circuits

Abstract-Comparison of unit cell coupling for grating‐gate and high electron mobility transistor array THz resonant absorbers

Journal of Applied Physics

Ajay Nahata, Ashish Chanana, Berardi Sensale-Rodriguez, Debdeep Jena, Hugo O. Condori Quispe, Huili Grace Xing, Jimy Encomendero, Mingda Zhu, Nicole Trometer, 

https://aip.scitation.org/doi/abs/10.1063/1.5032102

We report experimental studies on the excitation of synchronized plasmon resonances in AlGaN/GaN High Electron Mobility Transistor (HEMT) arrays. In contrast to the commonly employed grating-gate configurations, the analyzed structure contains periodically patterned ohmic contacts to the two-dimensional electron gas, which are laid-out parallel to the gate fingers. In this structure, the terahertz to plasmon coupling mechanism is fundamentally different from that in grating-gate configurations. Whereas the grating-gate configuration constitutes a coupled resonant system in which the resonance frequency depends on the grating periodicity, when periodical ohmic contacts are incorporated, the system behaves as a synchronized resonant system in which each unit cell is effectively independent. As a result, in a HEMT-array, the resonance is no longer set by the periodicity but rather by the gate and the ungated region length. Experimental results of fabricated samples compare well with numerical simulations and theoretical expectations. Our work demonstrates that the proposed approach allows: (i) more efficient excitation of high order plasmon modes and (ii) superior overall terahertz to plasmon coupling, even in configurations having less number of devices per unit area. From this perspective, our results reveal a simple way to enhance the terahertz to plasmon coupling and thus improve the performance of electron plasma wave-based devices; this effect can be exploited, for example, to improve the response of HEMT-based terahertz detectors.

Abstract-Comparison of unit cell coupling for grating‐gate and high electron mobility transistor array THz resonant absorbers

Journal of Applied Physics

Hugo O. Condori Quispe,   Ashish Chanana, Jimy Encomendero,Mingda Zhu, Nicole Trometer,  Ajay Nahata, Debdeep Jena,   Huili Grace Xing,Berardi Sensale-Rodriguez,

https://aip.scitation.org/doi/10.1063/1.5032102

We report experimental studies on the excitation of synchronized plasmon resonances in AlGaN/GaN High Electron Mobility Transistor (HEMT) arrays. In contrast to the commonly employed grating-gate configurations, the analyzed structure contains periodically patterned ohmic contacts to the two-dimensional electron gas, which are laid-out parallel to the gate fingers. In this structure, the terahertz to plasmon coupling mechanism is fundamentally different from that in grating-gate configurations. Whereas the grating-gate configuration constitutes a coupled resonant system in which the resonance frequency depends on the grating periodicity, when periodical ohmic contacts are incorporated, the system behaves as a synchronized resonant system in which each unit cell is effectively independent. As a result, in a HEMT-array, the resonance is no longer set by the periodicity but rather by the gate and the ungated region length. Experimental results of fabricated samples compare well with numerical simulations and theoretical expectations. Our work demonstrates that the proposed approach allows: (i) more efficient excitation of high order plasmon modes and (ii) superior overall terahertz to plasmon coupling, even in configurations having less number of devices per unit area. From this perspective, our results reveal a simple way to enhance the terahertz to plasmon coupling and thus improve the performance of electron plasma wave-based devices; this effect can be exploited, for example, to improve the response of HEMT-based terahertz detectors.

Abstract-Graphene-based reconfigurable terahertz plasmonics and metamaterials

Sara Arezoomandan^a, 

Hugo O. Condori Quispe^a, 

Nicholas Ramey^b, 

Cesar A. Nieves^c, 

Berardi Sensale-Rodriguez

http://www.sciencedirect.com/science/article/pii/S000862231630985X

This work discusses and compares two proposed practical approaches for realizing graphene-based reconfigurable terahertz metamaterials, namely: graphene-only plasmonic structures, and graphene/metal hybrid structures. From rigorous theoretical analysis, full-wave electromagnetic numerical simulations, as well as supporting experiments, several reconfigurable structures are analyzed and compared in terms of their: (i) Quality-factor, (ii) Extinction-ratio, (iii) Unit-cell dimensions, and (iv) Resonance-frequency tunability-range. From this analysis it is observed that at terahertz frequencies, although typically possessing larger unit-cell dimensions and being limited by a restricted resonance-frequency tunability-range, reconfigurable metamaterials based on graphene/metal hybrid structures can provide much larger quality-factors, extinction levels, and, when reconfigured, smaller extinction-level degradation than graphene-only plasmonic structures. As a result, when analyzed in the context of reconfigurable terahertz metamaterials, graphene might result attractive as a reconfigurable media providing tunability to otherwise passive metallic structures rather than as a reconfigurable plasmonic material per-se.

Abstract-Terahertz amplification in RTD-gated HEMTs with a grating-gate wave coupling topology

Hugo O. Condori Quispe1, Jimy J. Encomendero-Risco2,3, Huili Grace Xing2,3 and Berardi Sensale-Rodriguez1


1 The University of Utah, Salt Lake City, Utah 84112, USA
2 University of Notre Dame, Notre Dame, Indiana 46556, USA
3 Cornell University, Ithaca, New York 14853, USA
Appl. Phys. Lett. 109, 063111 (2016); http://dx.doi.org/10.1063/1.4961053
http://scitation.aip.org/content/aip/journal/apl/109/6/10.1063/1.4961053?TRACK=RSS

We theoretically analyze the operation of a terahertz amplifier consisting of a resonant-tunneling-diode gated high-electron-mobility transistor (RTD-gated HEMT) in a grating-gate topology. In these devices, the key element enabling substantial power gain is the efficient coupling of terahertz waves into and out of plasmons in the RTD-gated HEMT channel, i.e., the gain medium, via the grating-gate itself, part of the active device, rather than by an external antenna structure as discussed in previous works, therefore potentially enabling terahertz amplification with associated power gains >40 dB.