Proximity effects at the interface of a superconductor and a topological insulator in NbN - Bi_2Se_3 thin film bilayers

Abstract

In a search for a simple proximity system of a topological insulator and a superconductor for studying the role of surface versus bulk effects by gating, we report here on a first step toward this goal, namely the choice of such a system and its characterization. We chose to work with thin film bilayers of grainy 5 nm thick NbN films as the superconductor, overlayed with 20 nm thick topological layer of $\mathrm{B}{\mathrm{i}}_2\mathrm{S}{\mathrm{e}}_3$ and compare the transport results to those obtained on a 5 nm thick reference NbN film on the same wafer. Bilayers with ex-situ and in-situ prepared $\mathrm{NbN}-\mathrm{B}{\mathrm{i}}_2\mathrm{S}{\mathrm{e}}_3$ interfaces were studied and two kinds of proximity effects were found. At high temperatures just below the superconducting transition, all bilayers showed a conventional proximity effect where the topological $\mathrm{B}{\mathrm{i}}_2\mathrm{S}{\mathrm{e}}_3$ suppresses the onset or mid-transition $T_c$ of the superconducting NbN films by about 1 K. At low temperatures, a cross-over of the resistance versus temperature curves of the bilayer and reference NbN film occurs, where the bilayers show enhancement of $T_c(R=0)$, $I_c$ (the supercurrent) and the Andreev conductance, as compared to the bare NbN films. This indicates that superconductivity is induced in the $\mathrm{B}{\mathrm{i}}_2\mathrm{S}{\mathrm{e}}_3$ layer at the interface region in between the NbN grains. Thus an inverse proximity effect in the topological material is demonstrated.

arXiv comment8 pages, 11 figures

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Cited by in corpus (7)

• Proximity-effect-induced Superconducting Gap in Topological Surface States - A Point Contact Spectroscopy Study of NbSe2/Bi2Se3 Superconductor-Topological Insulator Heterostructures
• Observation of the superconducting proximity effect in the surface state of SmB6 thin films
• The origin of bias independent conductance plateaus and zero bias conductance peaks in Bi2Se3/NbSe2 hybrid structures
• Magnetic proximity effect of a topological insulator and a ferromagnet in thin film bilayers of $BiSbT{e}_3$ and $SrRu{O}_3$
• Conduction spectroscopy of a proximity induced superconducting topological insulator
• Magnetoresistance and gating effects in ultrathin NbN-$\mathrm{B}{\mathrm{i}}_2\mathrm{S}{\mathrm{e}}_3$ bilayers
• Strongly suppressed superconducting proximity effect and ferromagnetism in trilayers of $\mathrm{B}{\mathrm{i}}_2\mathrm{S}{\mathrm{e}}_3$ / $\mathrm{SrRu}{\mathrm{O}}_3$ / underdoped $\mathrm{YB}{\mathrm{a}}_2\mathrm{C}{\mathrm{u}}_3{\mathrm{O}}_{\mathrm{x}}$: A possible new platform for Majorana nano-electronics