Enhanced Superconductivity and Infinite Electro-resistance in Proximity Exchange Coupled Superconductor Nano-bridges by Electric Field - towards First Generation of Triplet Paired Superconductor FETs*

Recent breakthrough experiments on BCS superconductor based nano-bridges showed electric field control of the critical current (I_c) [1]. Their fundamental interest and high potential for cryogenic-nanoelectronics with this new type of all-metallic superconducting field-effect transistors (SuFETs) make them highly attractive. Here, we present results of gating experiments on superconducting thin NbN film (T_c ~12 K) based nano-SuFETs which show a tunable infinite electro-resistance (ER). Interestingly, we observe an enhancement in the I_c in stark contrast to the earlier work where a suppression of I_c was seen [1]. The observed ER is a consequence of a monotonic enhancement of the I_c (~25%) on applying electrostatic field through back-gate voltage in the range of ±30 V. Importantly, similar results are obtained in proximity coupled NbN/ferromagnetic-insulator nano-bridges. The ability to tune the superconducting properties of NbN layer with magnetic and electric fields will be discussed. This could lead to a novel triplet superconductor with exchange field [2] based SuFETs.

[1] De Simoni, G et al., Nat. Nanotechnol. 13, 802 (2018).
[2] Bergeret, FS, Volkov, AF & Efetov, KB, Rev. Mod. Phys. 77, 1321 (2005).