Faculty of Physics: Research Data

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  • Research Data
    8x8 Patch-Antenna-Coupled TeraFET Detector Array for Terahertz Quantum-Cascade-Laser Applications
    2024-04-10
    North, Nicholas K.
    Horbury, Michael D.
    Kondawar, Sanchit
    Kundu, Iman
    Salih, Mohammed
    Krysl, Anastasiya
    Li, Lianhe
    Linfield, Edmund H.
    Freeman, Joshua R.
    Valavanis, Alexander
    Lisauskas, Alvydas
    Roskos, Hartmut G.
    Monolithically integrated, antenna-coupled field-effect transistors (TeraFETs) represent sensitive and fast detectors operable at room temperature, designed to detect radiation across the terahertz range (0.3~THz to 10~THz). For this study, we conducted an experimental characterization of a single monolithically integrated patch-antenna coupled TeraFET optimized for maximum sensitivity at 3.4~THz. This characterization utilized a single-mode high-power terahertz Quantum-Cascade-Laser (QCL) emitting at the designated frequency. Subsequently, we integrated 8x8 of the aforementioned monolithically integrated patch-antenna-coupled TeraFET elements into a parallel readout circuitry, facilitated by the process maturity of a commercial 65-nm process node. This configuration, referred to as the "multi-element" terahertz detector, stands in contrast to conventional detector matrices where each TeraFET represents a pixel. Here, the entire TeraFET network operates as a unified pixel, amalgamating the output signals of all rectifying elements. For the multi-element detector presented here, we emphasize two significant enhancements for sensitive power detection experiments involving a 2.85~THz and a 3.4~THz single-mode quantum-cascade laser (QCL). First, the larger effective detector area improves detector alignment and signal stability with regards to vibrations. Additionally, the 8x8 array configuration provides a significantly reduced source-drain resistance of approximately 300~$\Omega$ at the most sensitive working bias point, which is determined to be at a gate-source bias of approx. 0.6~V in case of the single element. The decreased load impedance results in a substantial reduction in (thermal) detector noise and an increase in the attainable modulation bandwidth, particularly when coupled with a low-noise voltage amplifier circuit. Building upon the introduced approaches, we present a TeraFET-based detector system implementation that achieves a -3~dB modulation bandwidth of 15~MHz around the most sensitive bias point, with the potential to extend up to 20~MHz by further reducing detector impedance through adjustments in the applied gate potential (as depicted in \autoref{fig:RDS_noise_analysis}). Finally, we validate the system's performance using high-resolution spectroscopy data to investigating methanol vapor around 3.4~THz.
      4  34
  • Research Data
    Phonon renormalization and Pomeranchuk instability in the Holstein model
    2024-01-09
    The Holstein model with dispersionless Einstein phonons is one of the simplest models describing electron-phonon interactions in condensed matter. A naive extrapolation of perturbation theory in powers of the relevant dimensionless electron-phonon coupling λ0 suggests that at zero temperature the model exhibits a Pomeranchuk instability characterized by a divergent uniform compressibility at a critical value of λ0 of order unity. In this work, we re-examine this problem using modern functional renormalization group (RG) methods. For dimensions d>3 we find that the RG flow of the Holstein model indeed exhibits a tricritical fixed point associated with a Pomeranchuk instability. This non-Gaussian fixed point is ultraviolet stable and is closely related to the well-known ultraviolet stable fixed point of ϕ3-theory above six dimensions. To realize the Pomeranchuk critical point in the Holstein model at fixed density both the electron-phonon coupling λ0 and the adiabatic ratio ω0/εF have to be fine-tuned to assume critical values of order unity, where ω0 is the phonon frequency and εF is the Fermi energy. However, for dimensions d≤3 we find that the RG flow of the Holstein model does not have any critical fixed points. This rules out a quantum critical point associated with a Pomeranchuk instability in d≤3.
      52  2
  • Research Data
    Theoretical Data: Growth of self-integrated atomic quantum wires and junctions of a Mott semiconductor
    Continued advances in quantum technologies rely on producing nanometer-scale wires. Although several state-of-the-art nanolithographic technologies and bottom-up synthesis processes have been used to engineer these wires, critical challenges remain in growing uniform atomic-scale crystalline wires and constructing their network structures. Here, we discover a simple method to fabricate atomic-scale wires with various arrangements, including stripes, X-junctions, Y-junctions, and nanorings. Single-crystalline atomic-scale wires of a Mott insulator, whose bandgap is comparable to those of wide-gap semiconductors, are spontaneously grown on graphite substrates by pulsed-laser deposition. These wires are one unit cell thick and have an exact width of two and four unit cells (1.4 and 2.8 nm) and lengths up to a few micrometers. We show that the nonequilibrium reaction-diffusion processes may play an essential role in atomic pattern formation. Our findings offer a previously unknown perspective on the nonequilibrium self-organization phenomena on an atomic scale, paving a unique way for the quantum architecture of nano-network.
      25  5