Superconducting thermomagnetic instabilities tuned through electric-field-controlled strain in Nb/PMN-PT/Nb hybrids

Electric-field-controlled piezoelectric strain has been used, recently, to modify the superconducting properties in a new class of piezoelectric/superconducting (PE/SC) hybrids. Here, we investigate the appearance of thermomagnetic instabilities (TMIs) and the respective modification of the critical current density (JC) through the application of electric field (Eex) in PE/SC hybrids. Specifically, the SC nanolayers are Nb (thickness, dSC= 20 nm) deposited on both surfaces of PE macroscopic crystals of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-PT) with optimum composition x = 0.31 (thickness, dPE= 0.5-0.8 mm). The appearance of TMIs and the modification of JC by Eex is studied for two PMN-PT crystals of drastically different surface roughness (Sa). In the case of the PMN-PT crystal with low Sa (on the order of a few tenths of nm) TMIs are absent so that JC does not change under the variation of Eex. On the contrary, in the case of the PMN-PT crystal with high Sa (on the order of a few hundreds of nm) Eex induces TMIs in the Nb nanolayers. Specifically, the number of TMIs exhibits a non-monotonic increase on Eex, thus causing a non-monotonic degradation of JC. These experimental data are interpreted in terms of the variation of both volume strain and surface roughness on Eex. This work highlights practical means to control the current-carrying capability of SC nanolayers through strain provided by PE substrates.