Nb and NbN nano structures for tunable superconductivity

David Wang Auditorium, 3rd floor Dalia Maydan Bldg
Mr. Itamar Holzman, M.Sc. Candidate

Mr. Itamar Holzman, M.Sc. Candidate

Department of Materials Science and Engineering
Solid State Institution



Quantum technologies has recently garnered much attention nationally and worldwide alike. Superconductors are materials that have no electric resistance thanks to quantum behavior that they exhibit, even at the macroscopic scale. Superconductors are thus significant for realizing quantum technologies, and have already proved useful for quantum communication and quantum metrology [1], while there is an ongoing effort to facilitate superconducting-based quantum computing devices. Although the absence of electric resistance of superconductors is attractive for various applications, it also hinders the ability to apply voltage on a superconductor and hence to facilitate them for three-terminal device, which are the traditional architecture of computing devices. Thus, there is a great need in developing methods to gate the superconducting state of superconductors, especially at the nanometer scale. A common way to tune superconductivity is by weakening superconductivity in specific areas (weak-links), e.g. in nanostructures. To measure the quantum state of the electrons in such a weak link, it is possible to let them interfere with an additional weak link that is connected in parallel. Such superconducting quantum interference devices (SQUIDs) are already in wide use, e.g. as MRI devices. Nevertheless, although the quantum state of electrons in such devices can be tuned macroscopically, e.g. with external magnetic field, limitations in accessing the weak link directly challenge the local tunability of the quantum state, encumbering the realization of advanced quantum technologies.

By processing thin (~30 nm) Nb films, we developed planar SQUIDs made in a single-lithography step. The unique geometry allowed us to approach the weak link directly and tune the superconducting quantum state locally (~45 nm) [2]. Next, we wanted to expand our accessibility to the weak link so that the approach would be from 3D and not only in the plane. Such expansion requires films thinner than those available for superconducting Nb films. Therefore, we optimized the growth conditions of ultra-thin (sub-10 unit cells) superconducting NbN films. Such structures allowed us to obtain an ultra-thin SQUID, in which the weak links are accessible for 3D tunability.

[1] Holzman, I. & Ivry, Y. (2018). Quantum materials for nanoscale quantum sensors: opportunities and challenges in superconducting nanowire single photon detectors. arXiv preprint:1807.09060.

[2] Winik, R., Holzman, I., Dalla Torre, E. G., Buks, E., & Ivry, Y. (2018). Local tuning of the order parameter in superconducting weak links: A zero-inductance nanodevice. Applied Physics Letters, 112(12), 122601.


Asst. Prof. Yachin Ivry