Alternating current-driven microwave loss modulation in a fluxonic metamaterial

Abstract

We introduce a fluxonic metamaterial on the basis of nanopatterned superconducting Nb microstrips and employ it for modulation and synthesis of quantized loss levels in the lower GHz range by a sine-wave quasistatic ac drive. The nanopatterns are uniaxial nanogrooves with identical and different slope steepness, which induce a pinning potential of the washboard type for Abrikosov vortices. For the fundamental matching field, when the location of vortex rows geometrically matches the nanogrooves, the following effects are observed: The forward transmission coefficient S 21 (f ) of the microstrips can be controllably modulated within a range of about 3 dB by the ac current. For the sample with symmetric grooves, depending on the choice of the operation point in the current-voltage curve, the shape and the duty cycle of the output signal can be tuned. For the sample with asymmetric grooves, depending on the ac amplitude, a sine-to-triangular or a sine-to-rectangular pulse shape conversion is observed. The possibility of synthesizing quantized loss levels by a serial connection of the two samples with different nanopatterns is exemplified and can be used for the development of multilevel excess-loss-based fluxonic devices.Keywords: microwave loss modulation, fluxonic metamaterial, pulse form synthesizer, Abrikosov vortices, nanopatterning, washboard pinning potential, vortex dynamics, depinning frequency, focused ion beam milling, niobium films, matching field 1 arXiv:1510.02432v1 [cond-mat.supr-con]

Upper Frequency Limits for Vortex Guiding and Ratchet Effects

“…[35][36][37] for reviews. In particular, vortex guiding and ratchet effects were investigated both experimentally [25,28,30,31,33,34,38] and * oleksandr.dobrovolskiy@univie.ac.at theoretically [22,24,26,29]. At kHz ac frequencies the vortex dynamics is known to be frequency-independent [39] and it begins to depend on the ac frequency in the MHz range [28,31,32,38].…”

Abrikosov fluxonics in washboard nanolandscapes

“…In panel (g) is exemplified synthesis of three different insertion loss levels by a serial connection of samples S and A for an ac current I = 50 mA and a frequency 3.02 GHz. After [109].…”

“…A low-frequency (3 Hz) ac current was used [109] for tailoring the mw excess loss levels by vortices. The sine waves of the input quasistatic currents are shown in Fig.…”

“…Quantum metamaterials comprised of networks of superconducting qubits based on Josephson junctions are used for exploring quantum effects in meta-atoms [117]. Tailoring microwave losses due to Abrikosov vortices in individual sections of superconducting transmission lines allows one to use them as building blocks for fluxonic metamaterials [109] enriching the large family of artificial media [118].…”

Reduction of Microwave Loss by Mobile Fluxons in Grooved Nb Films

“…[10] Recently, microwave-stimulated superconductivity has been observed in transient regimes in NbN films [7] and was demonstrated to improve the quality factor of superconducting microwave resonators. [8] When shaped in technology-relevant geometries, such as thin films, [14] nanowires, [15][16][17] thin-wall cylinders, [18] and nanotubes, [19][20][21] almost all superconductors fall into the class of type-II superconductors. In external magnetic fields, whose magnitude is between the lower and the upper critical field, these are penetrated by a lattice of Abrikosov vortices and the vortex dynamics determines their resistive response.…”