Mechanism linking interface piezoelectricity to aluminum’s superconducting transition

Determine the microscopic mechanism that links the observed rapid enhancement of the interface piezoelectric transduction at the aluminum–silicon interface near T ≈ 1.2 K to the superconducting phase transition of aluminum. Specifically, establish how the superconducting transition of aluminum affects the interfacial electromechanical coupling quantified by the microwave transmission coefficient ratio Δ|S21,0| = |S21,0^Si| / |S21,0^AlN| measured for aluminum-on-silicon interdigital transducers relative to aluminum-on-aluminum nitride controls.

Background

To probe temperature dependence, the authors compare aluminum-on-silicon interdigital transducers (IDTs) to aluminum-on-aluminum nitride controls, defining Δ|S21,0| = |S21,0^Si|/|S21,0^AlN| to factor out calibration uncertainties and capture the interface piezoelectric response. The ratio shows a non-monotonic temperature dependence and exhibits a rapid enhancement around T = 1.2 K, coincident with the superconducting transition temperature of aluminum.

Understanding the microscopic origin of this enhancement is important because the paper establishes interface piezoelectricity as a significant, linear dissipation channel for superconducting qubits on silicon, with predicted quality-factor limits comparable to state-of-the-art devices. Clarifying the mechanism would inform both accurate modeling of electromechanical surface losses and strategies for materials and phononic engineering to mitigate qubit decoherence.