SUPERconducting silicon Resonators – SUPERR

We propose a fundamental study, coupled with the exploration of first applications, of the high frequency properties of heavily boron doped superconducting silicon.
This non-equilibrium material, synthesized for the first time in our group, is very stable and is obtained by laser doping. We have previously studied its properties and measured its main parameters in the 3D configuration (~ 100 nm thick). However, superconductivity could also be observed in the 2D limit (thickness <50 nm).
The prospects opened by the recent demonstration of all-silicon Josephson junctions and SQUIDs lead us to investigate the RF properties, largely unknown but fundamental for a superconducting quantum electronics of major impact for quantum information. This study is particularly relevant as the feasibility of silicon spin qubits has recently been demonstrated. In this context, the contribution of superconducting silicon resonators will be crucial for a scalable, integrated technology. The RF resonators needed are coplanar waveguides (CPW) and lumped resonators (formed by inductive meanders and interdigitated capacitors), and constitute the core of SUPERR project.
We will first study the parameters for the appearance of superconductivity in layers and wires a few nanometers thick in the 2D and 1D limits and characterize their superconducting properties. The amount and not the dopant concentration being the dominant parameter, high concentrations of boron atoms randomly scattered by the laser, are necessary and will induce a disorder in the thin Si:B layers, not necessarily negative according to our preliminary results but inducing a competition between localization (insulator) and Cooper pairs (supra) with a transition that we will try to highlight.
We will test the influence of a gate potential on superconducting silicon, boosted by the carrier density 100-1000 times lower than in a metal. Field effect modulation of silicon superconducting properties (DC or RF) could prove to be the key for the design of applications.
The study of high-frequency properties of resonators with temperature, doping and layer thickness provides access to the mechanisms of loss and the lifetime of quasiparticles, highlighting possible deviations of the BCS theory when switching from a 3D to 2D regime. In addition, we will probe the evoked gate effects in an attempt to modulate the resonance properties.
Finally, we will test the practical possibility to achieve Kinetic Inductance Detectors (KID) for the highly sensitive detection of astronomical photons, promising devices as Si has easily adjustable superconducting Tc and normal state resistance as well as a large kinetic inductance.
Thanks to this project, the physics of a disordered covalent superconductor with a low number of carriers will be better understood, simultaneously inducing progress in superconducting silicon applications.