Seminar: The non-recripical Josephson Effect

Prof. Ying Liu , The Pennsylvania State University will be visitng KTH on Friday, Sept 27. He will give the Friday Nano-Quantum Fika semiar. Fika at 14:45, Nanolab walk-through at 15:00, seminar at 15:15. Contact his host David Haviland if you would like to meet with Prof. Liu.

Electrically controllable nonreciprocal Josephson effect in planar tunnel junctions

Nonreciprocal Josephson effect, known also as the Josephson diode effect, in which zero-voltage supercurrents flow preferably in one direction, has been predicted in various Josephson junctions. However, electrically controllable, nonreciprocal Josephson tunnel junctions (as opposed to superconducting weak links) prepared by techniques compatible with technological applications such as superconducting-electronics-based quantum technologies are yet to be demonstrated. We have fabricated high-quality planar Josephson tunnel junctions featuring a composite tunnel barrier of Al₂O₃ and Hf_1-xZr_xO₂ using complementary-metal-oxide-semiconductor (CMOS) compatible atomic layer deposition techniques. These JTJs were found, unexpectedly, to show nonreciprocal Josephson effect in zero magnetic fields with the nonreciprocity controlled by an electric training current well above the critical current in zero magnetic fields. The quasiparticle tunneling spectra were found to show features associated with superconducting energy gaps of the two superconducting electrodes but without any nonreciprocal effects. I will offer a tentative explanation of the observed effects based on the presence of negative Josephson couplings.