Microwave photoassisted dissipation and supercurrent of a phase-biased graphene-superconductor ring

Letter
Open Access

Microwave photoassisted dissipation and supercurrent of a phase-biased graphene-superconductor ring

Ziwei Dou, Taro Wakamura, Pauli Virtanen, Nian-Jheng Wu, Richard Deblock, Sandrine Autier-Laurent, Kenji Watanabe, Takashi Taniguchi, Sophie Guéron, Hélène Bouchiat, and Meydi Ferrier

Phys. Rev. Research 3, L032009 – Published 8 July 2021

Abstract

Irradiating normal-superconducting junctions with microwave photons produce spectacular effects, such as Shapiro steps and photoinduced modifications of the dc supercurrent. Moreover, microwave irradiation can also have other, hitherto unexplored consequences, such as a photoassisted dissipation which is phase dependent. Here we present a finite-frequency measurement of both the dissipation and the supercurrent of a phase-biased graphene-superconductor junction in response to microwave photons. We find that, while the supercurrent response is well described by existing theory, the dissipation exhibits unexpected effects which need new theoretical elucidation. Especially with high frequency photons, the dissipation is enhanced at phase zero, where it is minimum without irradiation. We attribute this enhancement to Andreev level transitions, made possible by microwave-induced nonequilibrium population of Andreev bound states. Our results demonstrate that dissipation is a more sensitive probe of microwave photons than is the supercurrent, and reveal the potential of measuring dissipation to improve superconducting photodetectors and investigate photoassisted physics in hybrid superconducting systems.

Received 21 November 2020
Accepted 21 May 2021

DOI:https://doi.org/10.1103/PhysRevResearch.3.L032009

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

Published by the American Physical Society

Physics Subject Headings (PhySH)

Dissipative dynamics Proximity effect Superconducting RF

Graphene Superconducting devices

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Ziwei Dou ¹, Taro Wakamura¹, Pauli Virtanen ², Nian-Jheng Wu^1,3, Richard Deblock ¹, Sandrine Autier-Laurent¹, Kenji Watanabe ⁴, Takashi Taniguchi⁴, Sophie Guéron¹, Hélène Bouchiat¹, and Meydi Ferrier¹

¹Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405 Orsay, France
²Department of Physics and Nanoscience Center, University of Jyväskylä, Jyväskylä, Finland
³Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d'Orsay, 91405 Orsay, France
⁴National Institute for Materials Science, Tsukuba, Japan

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Issue

Vol. 3, Iss. 3 — July - September 2021

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Images

Figure 1
CPRs without microwave irradiation: (a) SEM images of the device. Left: a section of the MoRe resonator. Scale bar: $100 μ m$ . Inset: schematic of the graphene-superconductor ring. Right: zoomed-in image of the SGS junction. Scale bar: $3 μ m$ . Purple and magenta dashed outlines: top and bottom BN. White dashed outline: graphene. (b) Circuit diagram. For explanation, see text. (c) CPRs at $V_{g} = 2 V$ , and $T = 12$ mK, 0.9 K, and 1.5 K. Inset: $χ^{'} (Φ)$ . (d) The critical current $I_{c}$ versus $T$ at $V_{g} = 2 V$ . Dashed line: fitting to diffusive model with $E_{T h} = 34 μ eV$ . Inset: the amplitudes of the first three Fourier coefficients of the CPRs $| I_{c, n} |$ ( $n = 1, 2, 3$ ) versus $T$ . (e) $| I_{c, n} |$ ( $n = 1, 2, 3$ ) versus $V_{g}$ at $T = 12 mK$ .
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Figure 2
Effects of microwave irradiation on CPR Fourier coefficients: (a) CPRs with irradiation $ν = 2 GHz$ . The irradiation power is converted to the normalized value $s = α e V_{p k} / h ν$ in parentheses (see text). The sign reversal of $I_{s}$ is observed at $s \sim$ 1.2 with halved periodicity. (b) CPRs with $ν = 19 GHz$ . The sign reversal of $I_{s}$ is also seen at $s \sim 1.2$ , but without halved periodicity. (c), (d) $I_{c, 1} (s)$ and $I_{c, 2} (s)$ . All data are taken at $V_{g} = 2$ V and $T = 12 mK$ . (e), (f) Calculated $I_{c, 1} (s)$ and $I_{c, 2} (s)$ from Usadel equations with finite relaxation rate $γ = 1.2 E_{T h}$ . $k_{B} T = 0.004 γ$ . $Δ / E_{T h} = 50$ . Bessel functions $I_{c, 1} (0) J (2 s)$ and $I_{c, 2} (0) J (4 s)$ are plotted for (c), (e) and (d), (f), respectively (dashed lines). $J$ is the zeroth order Bessel function of the first kind. $I_{c, 1} (0) = 44 nA$ , and $I_{c, 2} (0) = - 9$ nA are the nonirradiated values from Fig. 1.
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Figure 3
Effects of microwave irradiation on the dissipative part of the susceptibility: (a) $χ^{″} (Φ)$ without irradiation at $T = 12 mK$ , 0.9 K, and 1.5 K, taken simultaneously as $χ^{'} (Φ)$ leading to the CPRs in Fig. 1. (b) $χ^{″} (Φ)$ taken simultaneously as the CPRs in Fig. 2. The irradiation frequency $ν = 2 GHz$ . The irradiation power is converted to the normalized value $s$ as in Fig. 2. The black dashed line is the $χ^{″} (Φ)$ without irradiation. $χ^{″} (Φ)$ shows no significant $Φ$ dependence under irradiation. (c) $χ^{″} (Φ)$ taken simultaneously as the CPRs in Fig. 2. $ν = 19 GHz$ . $χ^{″} (Φ)$ changes from $2 π$ periodic with no irradiation to $π$ periodic under higher irradiation power. (d) Left: $δ χ^{″}$ normalized by unirradiated value ( $s = 0$ ). Right: $I_{s}$ in Fig. 2 normalized by critical current at $s = 0$ . $V_{g} = 2$ V and $T = 12 mK$ for (b), (c), and (d). The $χ^{″}$ curves are shifted vertically for clarity.
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Figure 4
Calculation of $χ^{″} (Φ)$ with nonequilibrium distribution function: (a) Andreev spectrum of a long diffusive system displaying a minigap $E_{g} \sim 0.2 Δ$ . $Δ$ is the superconducting pairing potential. Side plot: distribution function change $δ f (E)$ due to irradiation (see text). (b) The interband term $| J_{1, - 1} |^{2}$ (red) and the intraband term $| J_{23, 44} |^{2}$ (blue). The corresponding transitions are marked by the arrows in the same colors in (a). (c) $χ_{0}^{″} (φ)$ calculated with $f_{F D} (E)$ (dashed line) and $χ_{\pm h ν}^{″} (φ)$ calculated with $f_{F D} (E \pm h ν)$ (dashed-dotted line). (d) Total $χ^{″} (Φ)$ . $σ$ stands for the irradiation power ( $σ = 0$ being no irradiation). Curves are offset for clarity. Similar to experiment, $k_{B} T = h ν_{r} = 0.01 Δ ≪ E_{g}$ , relaxation rate $h γ = 0.15 Δ \sim 0.5 E_{g}$ , and irradiation frequency $h ν = 0.5 Δ \sim 2 E_{g}$ . System size: $W \times L = 50 \times 30$ sites.
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