Proximity Eliashberg theory of electrostatic field-effect doping in superconducting films

Ummarino, Giovanni; Piatti, Erik; Daghero, Dario; Sklyadneva, I. Yu.; Chulkov, Eugene V.; Heid, R.

doi:10.1103/physrevb.96.064509

Cited by 31 publications

(47 citation statements)

References 54 publications

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“…While the agreement is clearly sound from a qualitative point of view, care has to be taken with assuming this to be a true quantitative estimation: first, this heuristic comparison neglects the "stretching" of the accumulation layer towards the potential barrier for large fields; second, different choices of the perturbation threshold may lead to different estimations of the number of atomic layers involved. On the other hand, we stress that the experimental values are determined employing a model assuming a simple step-like behavior for the induced charge density [23,46], which is an even rougher approximation of the real system.…”

Section: Discussionmentioning

confidence: 99%

Anomalous screening of an electrostatic field at the surface of niobium nitride

Piatti

Romanin

2018

Applied Surface Science

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The interaction between an electric field and the electric charges in a material is described by electrostatic screening, which in metallic systems is commonly thought to be confined within a distance of the order of the Thomas-Fermi length. The validity of this picture, which holds for surface charges up to ∼ 10 13 cm −2 , has been recently questioned by several experimental results when dealing with larger surface charges, such as those routinely achieved via the ionic gating technique. Whether these results can be accounted for in a purely electrostatic picture is still debated. In this work, we tackle this issue by calculating the spatial dependence of the charge carrier density in thin slabs of niobium nitride via an ab initio density functional theory approach in the field-effect transistor configuration. We find that perturbations induced by surface charges 10 14 cm −2 are mainly screened within the first layer, while those induced by larger surface charges ∼ 10 15 cm −2 can penetrate over multiple atomic layers, in reasonable agreement with the available experimental data. Furthermore, we show that a significant contribution to the screening of large fields is associated not only to the accumulation layer of the induced charge carriers at the surface, but also to the polarization of the pre-existing charge density of the undoped system.

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Section: Discussionmentioning

confidence: 99%

Anomalous screening of an electrostatic field at the surface of niobium nitride

Piatti

Romanin

2018

Applied Surface Science

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“…(23), we here set q(z) = 1, to account for the expectation that likely for the true screening length λ T F k F 1. The second-order correction (24) is neglibile for these parameters, being higher order in λ 2 T F eE/(Lω c ), and the nonlinearity visible in the result originates from g(ξ).…”

Section: A Size Effect In Electric Fieldmentioning

confidence: 97%

“…16 for a historical review), and the effect of electric fields on superconducting surfaces are theoretically discussed in several works. [17][18][19][20][21][22][23][24] In these, effects on the amplitude of superconductivity (T c ) are usually related to modulation of electronic density of states (DOS), which is also what contributes to the quantum size effects. A common approach is to consider "surface doping" and assume the DOS is modified within a Thomas-Fermi screening length from the surface.…”

Section: Introductionmentioning

confidence: 99%

Superconducting size effect in thin films under electric field: Mean-field self-consistent model

2019

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We consider effects of an externally applied electrostatic field on superconductivity, selfconsistently within a BCS mean field model, for a clean 3D metal thin film. The electrostatic change in superconducting condensation energy scales as µ −1 close to subband edges as a function of the Fermi energy µ, and follows 3D scaling µ −2 away from them. We discuss nonlinearities beyond gate effect, and contrast results to recent experiments.

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“…Starting from the 50s several gating experiments showed the impact of electrostatic charging on the conductivity of metallic thin films [1][2][3] and on the transition temperature of metallic superconductors [4,5]. Furthermore, recent calculations about gating on a metallic superconductor (Pb) showed that the electric field penetrates for a maximum depth of a few times the Thomas-Fermi length and the perturbation to superconductivity extends into the bulk of the superconductor for at least one coherence length [6]. Conventional solid gating allows to realize electric fields of the order of maximum 10 9 V/m.…”

Section: Introductionmentioning

confidence: 99%

Magnetotransport Experiments on Fully Metallic Superconducting Dayem-Bridge Field-Effect Transistors

Simoni²,

et al. 2019

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In the last 60 years conventional solid and electrolyte gating allowed sizable modulations of the surface carrier concentration in metallic superconductors resulting in tuning their conductivity and changing their critical temperature. Recent conventional gating experiments on superconducting metal nano-structures showed full suppression of the critical current without variations of the normal state resistance and the critical temperature. These results still miss a microscopic explanation. In this article, we show a complete set of gating experiments on Ti-based superconducting Dayem bridges and a suggested classical thermodynamic model which seems to account for several of our experimental findings. In particular, zero-bias resistance and critical current IC measurements highlight the following: the suppression of IC with both polarities of gate voltage, the surface nature of the effect, the critical temperature independence from the electric field and the gate-induced growth of a sub-gap dissipative component. In addition, the temperature dependence of the Josephson critical current seems to show the transition from the ballistic Kulik-Omelyanchuck behavior to the Ambegaokar-Baratoff tunnel-like characteristic by increasing the electric field. Furthermore, the IC suppression persists in the presence of sizeable perpendicular-to-plane magnetic fields. We propose a classical thermodynamic model able to describe some of the experimental observations of the present and previous works. Above all, the model grabs the bipolar electric field induced suppression of IC and the emergence of a sub-gap dissipative component near full suppression of the supercurrent. Finally, applications employing the discussed effect are proposed.

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Proximity Eliashberg theory of electrostatic field-effect doping in superconducting films

Cited by 31 publications

References 54 publications

Anomalous screening of an electrostatic field at the surface of niobium nitride

Anomalous screening of an electrostatic field at the surface of niobium nitride

Superconducting size effect in thin films under electric field: Mean-field self-consistent model

Magnetotransport Experiments on Fully Metallic Superconducting Dayem-Bridge Field-Effect Transistors

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