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 (J C ) through the application of electric field (E ex ) in PE/SC hybrids. Specifically, the SC nanolayers are Nb (thickness, d SC = 20 nm) deposited on both surfaces of PE macroscopic crystals of (1-x)Pb(Mg 1/3 Nb 2/3 )O 3 -xPbTiO 3 (PMN-PT) with optimum composition x = 0.31 (thickness, d PE = 0.5-0.8 mm). The appearance of TMIs and the modification of J C by E ex 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 J C does not change under the variation of E ex . On the contrary, in the case of the PMN-PT crystal with high Sa (on the order of a few hundreds of nm) E ex induces TMIs in the Nb nanolayers. Specifically, the number of TMIs exhibits a non-monotonic increase on E ex , thus causing a non-monotonic degradation of J C . These experimental data are interpreted in terms of the variation of both volume strain and surface roughness on E ex . This work highlights practical means to control the current-carrying capability of SC nanolayers through strain provided by PE substrates.