Microwave Admittance of Gold‐Palladium Nanowires with Proximity‐Induced Superconductivity

Abstract

measurements. [8,9] Shapiro steps, supercurrent enhancement, and other non-equilibrium effects under intense microwave irradiation have also been extensively studied. [1,[10][11][12][13][14][15][16] In contrast, the near-equilibrium response of superconductor-normalmetal-superconductor (SNS) junctions to weak microwave radiation has become an active area of investigation only recently. [17][18][19][20][21] While the adiabatic contribution to the kinetic inductance can be calculated from the dc current-phase relation, at high frequencies both reactive and dissipative contributions arise also from other mechanisms, such as driven transitions between quasiparticle states and oscillation of the Andreev level populations. [18] Surprisingly, however, little experimental data has been published on the topic thus far. [22,23] The parameter regimes and materials studied in the published experiments are very sparse, hence limiting the extent to which theoretical predictions [17][18][19][20][21] can be tested. In practice, data on the effective inductance and losses also expedites the process of designing high-frequency SNS-junction-based circuits, such as the SNS nanobolometer. [24,25] Previous experimental studies [22,23] have probed flux-and temperature-dependent changes in the linear microwave response of a superconducting ring with a gold normal-metal inclusion. The superconducting ring consisted of ion-beamdeposited tungsten in the first experiments, [22] and sputterdeposited Nb with a thin Pd layer at the SN interface in the later experiments. [23] A single SNS ring was biased with a dc magnetic flux and coupled weakly to a multi-mode microwave resonator. By measuring flux-dependent shifts in the quality factors and resonance frequencies, the authors determined how the complex-valued electrical susceptibility χ changes. [22,23] The change in χ, as a function of flux and temperature, was reported to be in excellent agreement with theoretical predictions based on Usadel equations and numerical simulations. However, the implicit offsets in both the real and imaginary parts of the reported susceptibility prevent a comparison to the theoretically predicted absolute values of Re In this article, we present measurements of the SNS junction admittance Z -1 (ω) = χ/iω for gold-palladium based junctions at angular frequencies ω of order 2π × 1 GHz. We use a chain of

Coherence-enhanced phase-dependent dissipation in long SNS Josephson junctions: Revealing Andreev bound state dynamics

“…A similar technique based on single mode resonators was already used for the investigation of short Josephson junctions embedded in superconducting rings [35][36][37]. More related to the present work, the impedance of an array of SNS dc SQUIDS was measured using a superconducting multimode resonator [38]. This work focused on the temperature dependence of the effective inductive and resistive components of the SNS SQUIDs whereas our work focuses instead of the phase dependence which bares most of the signature of the dynamics of Andreev states [14,16].…”

Phase-dependent microwave response of a graphene Josephson junction

“…2(b). We encounter no phase jumps and relate the external phase ϕ ext = n odd π (= n even π) to points of minimal (maximal) resonance frequencies [10,14]. Besides f 0 , the resonance lineshape also changes as seen in Fig.…”

“…8(a) one can verify this relation, since the relation between the experimentally deduced values of the susceptance B J and conductance G s obtained at ϕ = π for all different V bg -clearly follows a linear trend. Furthermore, the ratio B J /G s is the inverse loss tangent describing the quality of the Josephson inductance [14], where a larger ratio implies a more ideal behavior of the inductance. We attribute the cone-shaped spread in Fig.…”

“…The junction admittance can be probed as a function of phase by embedding a JJ in an rf SQUID that couples to a resonator [9][10][11][12][13]. The rf SQUID acts as a magnetic flux-tunable complex impedance in the circuit that shifts and broadens the resonate behavior, from which one can infer the phase-dependent inductive and dissipative response of the junction [14]. The strong demand for in-situ controllable junctions in microwave applications has raised the attention to JJs consisting of gate-tunable weak links [15].…”

Microwave calibration of qubit drive line components at millikelvin temperatures

“…Accurate determination of S-parameters in a cryogenic environment has wide applicability to the development of active and passive cryo-electronic devices with immediate impact on filtering 12 , interconnects 13 , multiplexers 14 , non-reciprocal devices 15 , single-flux-quantum-based technologies 16,17 , cryo-CMOS technologies 18 , quantum hardware packaging [19][20][21] , microwave impedance and waveform metrology 22 , and parametric amplifier development [23][24][25][26][27] , among others. Beyond quantum computing, scientific applications requiring accurate S-parameter characterization at low temperature include astrophysical observations 28 and high-frequency electronic transport experiments [29][30][31][32] .…”