Quasiparticle Spectroscopy, Transport, and Magnetic Properties of Nb Films Used in Superconducting Qubits

• DOI: 10.1103/physrevapplied.20.024031
• Publication Date: 2023-08-11T16:52:24Z
• Authors: Kamal R. Joshi; Sunil Ghimire; Makariy A. Tanatar; Amlan Datta; Jin-Su Oh; Lin Zhou; Cameron J. Kopas; Jayss Marshall; Josh Y. Mutus; Julie Slaughter; Matthew J. Kramer; James A. Sauls; Ruslan Prozorov
• Keywords: Superconductivity (cond-mat.supr-con); Quantum Physics; Condensed Matter - Superconductivity; 0103 physical sciences; FOS: Physical sciences; Quantum Physics (quant-ph); 01 natural sciences

Niobium thin films on silicon substrate used in the fabrication of superconducting qubits have been characterized using scanning and transmission electron microscopy, electrical transport, magnetization, London penetration depth - based quasiparticle spectroscopy, real-space real-time magneto-optical imaging. We study niobium to provide an example a comprehensive analytical set that may benefit circuits such as those quantum computers. The transition temperature ${T}_{c}=9.35$ K fairly clean gap. estimated superfluid density is enhanced at intermediate temperatures. These observations are consistent with recent theory anisotropic strong-coupling superconductivity $\mathrm{Nb}$ indicate outstanding quality. However, response magnetic field complicated, exhibiting significantly irreversible behavior insufficient heat dissipation (to substrate), leading thermomagnetic instabilities. This present challenge for further improvement transmon coherence. Possible mitigation strategies discussed.