Superconducting Transition Temperature Modulation in NbN via EDL Gating

Abstract

We perform electric double layer gating experiments on thin films of niobium nitride. Thanks to a cross-linked polymer electrolyte system of improved efficiency, we induce surface charge densities as high as ≈ 2.8 × 10 15 cm −2 in the active channel of the devices. We report a reversible modulation of the superconducting transition temperature (either positive or negative depending on the sign of the gate voltage) whose magnitude and sign are incompatible with the confinement of the perturbed superconducting state to a thin surface layer, as would be expected within a naïve screening model. Keywords EDL gating · Superconductivity · Thin films · Niobium nitride · ScreeningIn recent years, electric double layer (EDL) gating has become a popular tool in condensed matter physics to tune the chemical potential of a wide range of materials well beyond the capabilities of standard solid-gate field-effect devices. Indeed, the EDL that builds up at the interface between the active channel and a polymer electrolyte solution (or an ionic liquid) acts as an effective nanoscale capacitor with extremely high capacitance [1]. In the field of superconductivity, EDL

Ionic liquid gating of ultra-thin YBa2Cu3O7−x films

“…We note that, recently, a similar argument was raised by authors of Ref. 28 to account for their ability to reduce T c in 40 nm thick NbN films. The second scenario involves an electric field-driven redistribution of the oxygen atoms in the basal planes of YBCO, as proposed already in the 90s.…”

Towards the insulator-to-metal transition at the surface of ion-gated nanocrystalline diamond films

“…The electric transport properties of diamond-based EDL transistors have been extensively studied [12][13][14][15][16][17], but no evidence was reported for either SC or good metallic behavior. This can be associated with the relatively modest charge carrier densities achieved in these works on insulating single crystals and epitaxial thin films ( 7 ·10 13 cm −2 [12][13][14][15][16][17]) with respect to the values typically obtained in conducting systems (≃ 10 14 − 10 15 cm −2 [18][19][20][21][22][23][24]).…”

“…For each V G application, the induced charge density is ∆n 2D = Q EDL /(f r · S), where S is the surface area of the NCD film covered by the PES, f r is the rugosity determined via AFM, and Q EDL is the charge stored in the EDL as measured by double-step chronocoulometry. This is a well-established electrochemical technique [28] which has been employed to reliably determine ∆n 2D for a wide variety of materials [18][19][20][21][22][23].…”

Strong dopant dependence of electric transport in ion-gated MoS2

“…[30][31][32][33][34][35] Most of these results have been obtained within the electrostatic limit, i.e., by only accumulating ions at the material surface and exploiting the ultrahigh electric field that develops in the electric double layer (EDL). 36 However, ionic gating of layered materials allows for a further degree of freedom in the technique, by exploiting the electric field to intercalate the ions between the van der Waals-bonded layers, thus allowing control over the properties of the entire bulk.…”